Preheat your oven to 180C/160C Fan, and line three 8"/20cm cake tins with parchment paper.
Add your butter and sugar to a bowl, and beat until light and fluffy. I use my Kitchenaid with the paddle attachment!
Add in your flour, eggs and baking powder and beat again until a lovely smooth cake mixture is formed.
Split evenly between the three tins and bake in the oven for 30-35 minutes (or until a skewer comes out clean!)
Once baked, leave to cool in the tin for 10 minutes, and then leave to cool fully on a wire rack.
For the Buttercream
Beat your butter on its own for a while in your mixer until it's smooth and supple.
Add in your icing sugar a little at a time and beat fully until its light and fluffy!
Add in your Biscoff spread and beat until combined. If its really stiff, add in 1-3tbsp of boiling water mixing fully each time.
For the Ganache
Add your chocolate and cream to a microwaveable bowl, and heat for 15-30 second intervals at half power. Keep going and stiring each time until a smooth ganache is formed.
Alternatively, add your cream to a pan and heat till just before boiling point. Pour over finely chopped chocolate and leave to sit for 5 minutes. Once sat, mix till smooth (Add back to the pan if its not quite melted).
Leave the ganache in a bowl and stir every few minutes till it forms a peanut butter like consistency - you can do this in the fridge as well, just make sure to stir it so it doesn't set too quickly!
For the Decoration
Spread a smidge of buttercream on the cake board, and add your first cake to a cake board (for an 8" cake, I use a 10" board). Spread over some of the buttercream.
Add on the second cake, and repeat!
Add on the third cake - spread some of the buttercream on top and around the edges till the sides are smooth and you have created a crumb coat. It doesn't need to be thick, it just needs to fill any gaps or holes that may be on the sides!
Refrigerate the cake for 10-15 minutes to set the crumb coat.