Preheat the oven to 350°F (175°C). Lightly grease a 9x9-inch baking pan with nonstick baking spray or line it with parchment paper for easy removal.

In a large mixing bowl, whisk together the melted butter, granulated sugar, and brown sugar until fully blended. Add the eggs and vanilla extract, whisking vigorously until the mixture becomes smooth, light, and slightly frothy.

Sift in the cocoa powder, flour, espresso powder (if using), and salt. Using a rubber spatula or wooden spoon, fold the dry ingredients into the wet mixture just until no flour pockets remain—do not overmix.

Pour half of the brownie batter into the prepared pan, spreading it evenly to the edges. Drop spoonfuls of chilled Biscoff spread across the surface, distributing it evenly over the batter.

Spoon the remaining batter on top, gently smoothing it out to cover the Biscoff layer. If desired, dollop additional Biscoff spread over the top for extra flavor and visual appeal.

Transfer the pan to the oven and bake for 30 to 35 minutes, or until the center is just set. For ultra-gooey brownies, begin checking for doneness around the 25-minute mark and remove from the oven when the center is slightly underbaked but not liquid.

Let the brownies cool in the pan for about 20 minutes before transferring them to a wire rack to cool completely.

For an added finishing touch, melt extra Biscoff spread in the microwave for 20 to 30 seconds until smooth. Drizzle over the cooled brownies and garnish with crumbled Biscoff cookies before serving.