Start by lining an 8x8-inch baking pan with parchment paper, allowing some overhang for easy removal later. Next, place 200g of Biscoff cookie butter in the freezer to firm up while you move on to the oven.

Preheat your oven to 180°C (350°F), creating a warm environment for baking those Fudgy Biscoff Cookie Butter Brownies.

In a mixing bowl, whisk together brown sugar, granulated sugar, eggs, egg yolk, and vanilla extract until the mixture is smooth and well-combined.

In a saucepan, melt unsalted butter and semi-sweet chocolate chips over low heat, stirring continuously. Remove from heat and whisk in the Dutch cocoa powder.

Gently fold the melted chocolate mixture into the egg and sugar mixture, stirring until just combined.

Add in the all-purpose flour, espresso powder, and sea salt, folding them into the batter until no dry streaks remain.

Spread half of the brownie batter into the bottom of the prepared pan. Take your frozen Biscoff cookie butter and carefully place it on top, then spoon the remaining brownie batter over to cover completely.

Crumble the Biscoff cookies over the top of your brownie batter, pressing them in gently. Drizzle additional melted Biscoff cookie butter on top.

Place the pan in your preheated oven and bake for 30-40 minutes. To check for doneness, insert a toothpick.

Allow the brownies to cool completely in the pan on a wire rack. Once cooled, use the parchment overhang to lift them out and slice into squares.