Preheat an oven to 350 degrees, line a pan with baking sheet and grease its sides with butter.
Prepare the base: Place flour, baking powder and ground almonds in a bowl and mix well.
In a separate bowl mix egg yolks and vanilla extract with a manual whisk.
Whip the egg whites at high speed for approximately one minute until white whip begins to form. Gradually add sugar and continue whipping for approximately 2-3 minutes until you get a soft but stable whip. Add the egg yolk mixture to the egg whites whip and mix gently with a manual whisk until they are absorbed into the mixture.
Gradually add the whip to the flour and almonds mixture, one-third at a time, and fold using a spatula just until you get a uniform mixture. Be careful not to fold too much, so as not to cause the volume of batter to fall. Pour the batter into a pan and flatten its surface.
Bake for approximately 30 minutes until a toothpick stuck at the center of the cake comes out dry.
Remove from the oven and allow it to cool slightly. Pass a sharp knife around the sides and release the spring. Allow it to cool completely, wrap in plastic wrap and store at room temperature until the assembly.
Preparing the Irish Cream syrup: Bring the water and sugar to a boil in a small saucepan and cook for 2-3 minutes. Remove from the stove, add liqueur and mix well. Allow it to cool at room temperature.
Prepare the Biscoff Spread cream: Place the sweet cream, powdered sugar and Biscoff Spread into a mixer bowl and beat well using a manual whisk into a smooth batter. Assemble the batter and whip for 2-3 minutes until getting a stable whipped cream.
Assemble the cake: Cut the cake along its breadth into two equal layers using a long serrated knife (a bread knife). Brush the bottom layer with half of the syrup. Spread a thin layer of Biscoff Spread using a palette spatula (if the paste is too stiff, heat it for a few seconds beforehand in a microwave). Coat on top with half of the Biscoff Spread cream. Place another layer of cake and brush with the rest of the syrup. Spread another layer of Biscoff Spread and coat the top part of the cake with the remainder of the whipped cream. Keep refrigerated for two hours at least before serving.
Before serving: Decorate with Biscoff Cookie pieces. Refrigerate for up to 3 days.