Rhubarb Shortbread Cake
Time for rhubarb and shortbread feast!
If you love sweet/sour rhubarb and crumbly, buttery shortbread then you will love this bake!
So, what do we have here? Crumbly and buttery, enriched shortbread base layered with sweet/sour rhubarb mousse. On top of this buttery/sour/sweet goodness rests a good dose of fresh rhubarb, spiced with earthy cardamom and only lightly sweetened to keep its sour kick. All is covered with soft meringue cloud and crumbly, cookie-like shortbread topping. Did I mention that it’s going to be a feast?!
This rhubarb cake is easy to prepare. It’s a quick bake. Shortbread on the bottom and the top cover come from 1 dough (which gives two different textures when baked). In this recipe you will have two options - you can go with smooth rhubarb mousse plus fresh rhubarb (I love this version - prep time will be about 1 hour) or you can bake it using fresh rhubarb only (prep time will be about 30 min; all is included in the recipe).
This is quick, easy and simply delicious home baking!
For a good bake:
Shortbread base and topping come from one dough. It’s crumbly, buttery and enriched with egg yolks. Small amount of baking powder gives it a slight lift. For a good bake you want to swiftly incorporate cold butter into flour. Use your preferred option - food processor, pastry cutter or simply incorporate using finger tips and palms of your hands. The pastry will look slightly dry when combined. Don’t add any water. Bring the dough together using egg yolks only. Chill the dough for 1 hour (and up to 12 hours). When ready, no need to roll it out. Break the dough into few pieces and patch into the baking tin, even out using a tablespoon (see pictures). Reserve the rest of the dough for the topping (needs to be chilled until ready to use). Blind bake the base for the best texture.
Rhubarb - you will need 8 handsome rhubarb stalks for this cake (about 1.5kg). You may opt to bake using fresh rhubarb only (then go with 1 kg). It’s so worth to prepare the rhubarb mousse as you will have beautiful cake with few different, complementing textures. Fresh rhubarb layer - cut rhubarb into 0.5-1cm chunks. 1cm chunks will have more texture and bite to it. If you want the rhubarb to be more mellow - go with smaller chunks (0.5cm). Rhubarb filling in this cake has a real kick - it’s not too sweet, keeping the beautiful sour notes of rhubarb and mellowing it down with semi-sweet shortbread.
Rhubarb mousse/quick povidl - my mum used to bake few versions of this cake throughout the year. She was using povidl layer and then fresh fruit (or only povidl during the winter). So, what is povidl really and how it differs from jam or confiture? Povidl is a type of jam/confiture - just thicker, usually prepared over the course of 5-7 days. Cooked on and off for 20 minutes each day, hitting high temperatures (Maillard reaction gives it a specific, almost caramelised taste). By the end of cooking you will get thick fruit spread (used in tortes or Christmas/Easter bakes). On the internet (in English) most sources would interchangeably use plum povidl and povidl as one and the same thing - but povidl really can be made from any fruit. In my family it was usually: sour cherries, Damson plums, strawberries, gooseberries and rhubarb (veg). Going back to the recipe - here we are going for a super quick version (hence I’m calling it a mousse rather than real-deal povidl). What it has in common with povidl is - thick consistency and cooking at higher temperature. You may opt to cook it a day before baking and then cook one more time on the day of baking to reduce further. Just make sure to add cornflour as a last step, in the last 10-15 minutes of cooking (in the real povidl only fruit and sugar are cooked).
Meringue - beat egg whites with sugar to peaks (stiff but not too dry) and place on rhubarb 1 Tablespoon at a time to create little hills.
Top layer - grate shortbread on a large grater scale. Use chilled or frozen dough.
Storage - store your cake loosely covered with clean kitchen towel. This cake tastes best on the day it’s baked but is also enjoyable on day 2.
Other fruit - you can prepare similar cake using the same method and use various fruit. This method would suit sour cherries, Damson plums, peaches or gooseberries.
Rhubarb Shortbread Cake
Yield: 12-15 slices
Time: 30min-1hr prep + 35-40min baking
Rhubarb mousse (quick povidl):
5 large rhubarb stalks (1kg)
25g unsalted or salted butter
80g light brown or caster sugar
120ml freshly squeezed orange juice (from 1 large orange)
1/4 tsp ground cardamom
1 Tbsp (10g) cornflour
330g all purpose (plain) flour
227g unsalted butter, cold
90g caster sugar or granulated sugar
1/8 tsp table salt
1/2 tsp baking powder
3 large egg yolks
Fresh rhubarb layer (if you are not preparing mousse - double the portion) :
2-3 large rhubarb stalks (500g)
30g sugar (2 Tbsps)
15g vanilla sugar (1 Tbsp, or replace with regular sugar)
1/4 tsp ground cardamom
3 large egg whites, leftover
45g (3 Tbsps) sugar
1/8 tsp table salt
Prepare rhubarb mousse (quick povidl): Wash rhubarb and cut into 0.5-1cm pieces. In medium pot (the wider the better) melt butter and when starts sizzling add rhubarb, sugar and cook on medium-high heat for 7-10 minutes, stirring every so often. After that time add orange juice and cardamom. Cook for another 10-15 minutes on medium-high heat. Stir every so often and watch not to get burned as the mixture will be piping hot. After 25 minutes the mixture should thicken somewhat. Transfer small portion of hot mousse into a cup, add cornflour and mix until combined then add back to the mixture and stir. Cook for another 10 minutes until your rhubarb mousse thickens. You know the mixture is ready when the povidl sticks to the spoon for a split second, when turned upside down, before dropping. Cool the mixture fully before transferring onto the shortbread.
Prepare crumbly shortbread: Transfer flour into a mixing bowl, add small chunks of cold butter (you can also use grater to grate cold or frozen butter, or add small cubes of butter). Use food processor (few pulses) or pastry cutter or simply work butter into flour using your finger tips and palms of your hands until crumbly texture forms (with pea-sized chunks of butter). Try to be swift at it not to melt the butter. Add sugar, table salt, baking powder and mix swiftly. At the end add egg yolks. Mix briefly to combine and then bring the mixture into a cohesive dough. Rather than knead - try to press the dough with palms of your hands - just enough to bring the dough together. It will look a bit crumbly - that’s the way it should be, don’t add water or other liquid. Wrap in cling film and refrigerate for 1 hour (and up to 12 hours).
Blind bake the base: Brush the form with butter (sides and bottom), line the bottom with parchment paper. Divide the shortbread into half (place the other half back in the fridge). Break it into crumbly pieces and press into the bottom of the baking tin (if you need more than half of the dough - then just take small piece from the remaining dough). Even the surface out using a tablespoon. Dock the pastry (make few holes using fork). Place the tin with the pastry into the fridge or freezer for 30min. In a meantime preheat the oven to 180C (160C fan forced). When ready, bake the base for 20 minutes. When done, take out from the oven and cool down fully before proceeding. Leave the oven working at 180C (160C fan forced).
Prepare fresh rhubarb layer: Wash remaining rhubarb. Cut into 0.5-1cm (thinner pieces will go mellow during baking, thicker will have more texture to it after baking - I love thicker pieces!). Sprinkle 3 Tbsps of sugar and ground cardamom and toss chopped rhubarb to coat all the pieces. Set aside.
Prepare the foam: Beat 3 egg whites on low-medium speed for 1 minute. When egg whites become fluffy, start adding sugar - 1 Tablespoon at a time. Mix for 1-2 minutes until stiff peaks (firm but not too dry). At the end add a pinch of salt.
Assemble: Transfer cooled rhubarb mousse on top of the cooled shortbread base. Even out. Distribute evenly fresh rhubarb on top of the mouse. Using Tablespoon place meringue clouds/foam on top of fresh rhubarb (one Tablespoon at a time) - even out if needs be, trying to leave some little hills. Grate the remaining chilled shortbread dough on top of the foam. Place the tin in the oven.
Bake your rhubarb cake for 35-40 minutes at 180C (160C fan forced), until the top is golden brown and you can see rhubarb bubbling up on the sides of the tin. If you decided to bake this cake with fresh rhubarb only (double the portion, using 1 kg of rhubarb) then bake for 40-45 minutes (if you went with thicker pieces - bake for full 45 minutes).