Preheat the oven to 350°F and line baking trays with parchment paper. Whisk together the flour, baking soda, baking powder, salt, and cinnamon so the dry ingredients distribute evenly throughout the cookie dough.
Beat the softened butter, brown sugar, and granulated sugar until light and fluffy. Mix in the Biscoff spread, egg, egg yolk, and vanilla extract until the mixture becomes smooth and creamy.
Gradually combine the dry ingredients with the wet mixture, stirring gently until no dry flour remains. Fold in the crushed Biscoff cookies and white chocolate chips carefully to avoid overmixing.
Scoop the dough into large portions and chill for 30 minutes so the cookies bake thicker and develop deeper caramelized flavor during baking.
Arrange the chilled dough balls on baking trays with space between each one. Bake for 11–13 minutes until the edges are lightly golden but the centers still look slightly soft.
Drizzle warm Biscoff spread over the cookies while they are still warm, then cool for 10 minutes before serving for the best texture and flavor.