Banana Biscoff Cake

Preheat the oven to 180℃ (365℉) and line two 7.5-inch square baking trays with parchment paper (baking paper or greaseproof paper).
In a large mixing bowl, use an electric whisk to beat 240 g salted butter and 200 g demerara sugar. This is called "creaming." Continue until the mixture is light in colour and fluffy.
To the same bowl, add 2 large eggs and whisk into the batter.
Add 3 teaspoons full fat milk and 1 teaspoon vanilla extract, then beat until incorporated.
In a small bowl, use a fork to mash 3 overripe bananas until they form a paste. Add the banana paste to the cake batter.
Sieve 300 g self raising flour, ½ teaspoon cinnamon powder, and 1 teaspoon baking powder into the batter. Using a large spatula or baking spoon, cut through the middle and turn the batter. Repeat this motion (folding in) until everything is just mixed.
Pour the batter evenly between the two trays and bake until golden, about 20 to 30 minutes (depending on your oven). Test with a toothpick (if it comes out dry, the cake is done). Cool on a baking rack.
In a large bowl, use an electric whisk to beat 100 g butter and 100 g icing sugar. Now add 160 g smooth Biscoff spread and 1 tablespoon full fat milk. Mix. The icing is done.
Using a spatula, spread a thin layer of Biscoff buttercream between the cakes. Sandwich them on top of each other, then spread another layer on top. Use the leftover Biscoff buttercream to pipe swirls on top of the cake.