Start by preheating your oven to 350°F (175°C). Grease and flour your 9-inch round or square cake pan to ensure the cake doesn’t stick during baking.

In a medium-sized bowl, whisk together the flour, baking powder, and salt. Set aside.

In a separate large mixing bowl, beat the softened butter and granulated sugar with a hand or stand mixer until the mixture becomes light and fluffy. This will take about 3-4 minutes.

Add the egg and vanilla extract to the creamed butter and sugar mixture. Continue mixing until smooth.

Gradually add the dry ingredients into the wet ingredients, mixing until the batter is smooth. If the mixture seems too thick, add the milk, a tablespoon at a time, to reach a smooth, spreadable consistency.

Pour the batter into the prepared cake pan and spread it out evenly. Bake for 30-35 minutes, or until a toothpick inserted into the center of the cake comes out clean. Once done, allow the cake to cool in the pan for about 10 minutes before transferring it to a cooling rack to cool completely.

While the cake is cooling, make the buttercream. In a mixing bowl, beat the softened butter until smooth and creamy. Add the powdered sugar, one cup at a time, mixing well between each addition.

Beat in the vanilla extract and Biscoff cookie butter, ensuring that everything is well incorporated. In a separate bowl, beat the egg whites until soft peaks form. Gently fold the egg whites into the buttercream mixture to make it light and fluffy.

Once the cake has completely cooled, frost it generously with the Biscoff buttercream. You can spread it with a spatula or use a piping bag for a decorative touch.

After frosting, let the buttercream set for a while. Slice the cake, serve, and enjoy every sweet, buttery bite!