Preheat your oven to 180C/160C Fan, and line two deep 8"/20cm tins with parchment paper.
Add your butter, sugar, self raising flour and eggs to a stand mixer bowl (or other bowl if you don't have a stand mixer) and beat together until smooth.
Alternatively you can beat the butter and sugar until light and fluffy, and then add in the flour and eggs.
Fold through the fruit, and split between the two tins.
Bake in the oven for 40-45 minutes, or until baked through. Sometimes because of the fruit it can take a little longer to bake, so keep an eye on it. A skewer should come out clean, and the cake shouldn't bake a bubbling/crackling sound when out of the oven.
Once baked, leave to cool in the tin for 20-30 minutes, and then remove carefully and cool fully on a wire rack. I find it easier to keep the parchment paper on the bottom of the cake when cooling because of all the fruit.
For the Coulis
Whilst the cake is cooling, make your coulis. Alternatively, you can do this at any time and store it in the fridge.
Add your fruit to a medium sized pan. I cut the tops of my strawberries and halve/quarter them depending on their size so they're the same size as the raspberries.
Add your the sugar to the pan, and heat the mixture on a medium heat. Stir it often so the sugar doesn't catch, and mash the fruit down as it softens.
Blitz the mixture so its smoother, and then pass it through a sieve to get rid of any seeds/lumps.
Leave the coulis to cool fully. Store it in the fridge whilst not using for up to 4 days.
For the Buttercream
Beat room temperature unsalted butter (NOT SPREAD) for a few minutes so its really smooth and supple.
Add in the icing sugar and beat again.
Add in the coulis and beat until smooth.
For the Decoration
Put your first layer of your cake onto a plate, and slather on half of the buttercream.
Add the second layer of the cake, and slather on the rest of the buttercream.
Decorate the cake with the berries of your choice, and a drizzle more of the coulis!
Enjoy!
Notes
This cake should really be stored in the fridge because of the amount fresh fruit, but it does make it slightly firmer once refrigerated.
Its best on the day of baking.
Frozen berries will produce more liquid when baking so it might take longer to bake.
You can easily use any shop bought fruit coulis if you don't want to make it!
You can bake a smaller version of the cake by using two 8' tins and: