Preheat the oven to 180C (350F). Grease and line two 20cm | 8in layers cake tins – or spray with cake release. You can also use four 15cm | 6in cake tins for a taller cake.
Add the flour, sugar, cookie crumbs, baking powder, bicarbonate of soda and spice(if using) to a large mixing bowl or the bowl of a stand mixer fitted with the paddle attachment. Mix to combine.
Add all remaining ingredients – butter, eggs, milk, vanilla extract and beat together on low speed initially, increasing speed as ingredients combine.
Stop the mixer and scrapw the bottom and sides of the bowl with a spatula then mix again until batter is completely smooth.
Divide the batter between the prepared tins and level.
Bake for 30-35 minutes until a skewer inserted in the centre comes out clean. Leave to cool in the tin for 10 minutes then carefully turn out onto a wire rack. Cool completely before frosting.
Make The Butter Cream:
Put the Biscoff spread, butter (both need to be at room temperature), vanilla extract and salt in a bowl or the bowl of your stand mixer. Beat together until smooth.
Gradually add the icing sugar, beating of low speed initially so that it doesn't shower you with a cloud of sugar. Continue to beat until it is completely smooth and forming peaks, adding a little of the hot water, if needed.
Assemble The Cake:
Transfer the buttercream to a large piping bag fitted with a star tip.
Add a generous amount of frosting on your bottom cake layer and smooth. Top with the second layer and repeat.
Smooth the frosting over the top and sides of the cake. You can leave the cake showing through to achieve the 'naked' cake look or do a crumb coat then chill the cake. Add another layer of frosting and smooth over the cake.
Decorate The Cake:
Heat the Biscoff spread in the mircrowave for 20-30 seconds and stir until smooth and runny.
Drizzle this around the perimeter of the cake, letting it drip prettily down the sides. You can use a spoon or a small squeeze bottle for this.
Spread the Biscoff over the top of the cake to cover (optional).
Pipe remaining buttercream over the top of the cake and decorate with the cookies.