Heat the oven to 180ºc/160ºc Fan and line three 20cm/8inch sandwich cake tins with baking parchment – leave to the side.
In a stand mixer, beat together the butter and caster sugar for a few minutes until light and fluffy. Add in the flour, eggs, and lemon zest and beat again briefly until combined – try not to overbeat!
Carefully fold through the 300g of fresh blueberries into the mixture.
Divide the mixture between the three tins and smooth it over – bake for 25-30 minutes until the cakes are golden and when the cake springs back (skewer should also come out clean)!
Once baked, leave the cakes to cool in their tins for 10 minutes or so, and then remove and leave to cool fully on a wire rack. If the cake has domed slightly, leave the cake to cool upside down to flatten it slightly so its easier to decorate later!
For the Decoration
Beat the butter with an electric mixer for a couple of minutes to loosen it – gradually add the icing sugar on a slow speed until it is combined, add the lemon juice, then speed the mixer up and mix for 3-4 minutes until thoroughly combined and smooth.
If its too thick, gradually add the boiling water until you reach the desired texture – I usually add 2 tablespoons! Keep on beating for 2-3 minutes until whipped and silky smooth!
Using your favourite piping tip, I used a large round tip, pipe the buttercream onto the bottom layer of the cake. Add some jam, I drizzle it slightly to make it look pretty, and add the second layer, and pipe buttercream on again, and then the jam again, and add the final cake layer.
I then pipe the rest of my buttercream on top, and add on some extra fresh blueberries!
Notes
This cake will last at room temperature for 3 days.