Turn the oven to 325 degrees F. Grease and flour a 13-by-9 inch pan and set aside.
Place flour, baking powder, and salt in a medium-size bowl and whisk together to mix.
With an electric mixer, beat the eggs one by one on a medium speed, for about 1 minute and slowly add the sugar until all sugar is incorporated. The egg mix will be very fluffy.
Slowly pour the melted butter and vanilla into the mixer.
Add the flour mixture and crushed biscoff cookies in batches and gently fold with a spatula until well combined. DO NOT OVER MIX.
Transfer batter to your prepared pan using a rubber spatula to help you spread the evenly. Bake for 30-35 minutes or until cake looks light golden or a wooden toothpick comes out clean when inserted into the cake.
Remove the cake and transfer to a wired rack to cool completely. Poke the top of the cake using a toothpick, skewer or fork all over.