Preheat the oven to 325F/163C convection (300F/149C conventional). Use cooking spray and parchment paper to grease and line an 8-inch square pan.
Align the Biscoff cookies along the bottom of the pan and set aside.
15 Lotus Biscoff Cookies
In a heat safe bowl or a saucepan, melt the butter with the semi-sweet chocolate. Set them aside to cool while you get the rest of the ingredients together.
3/4 cup (170g) unsalted butter, 1 cup (6oz) semi-sweet chocolate morsels
Use a whisk to combine the eggs, granulated sugar, brown sugar and vanilla until they're just barely combined; don't over-mix.
4 large eggs, 1 cup (200g) granulated sugar, 1/2 cup (95g) light brown sugar, 1 tsp vanilla extract
Slowly pour in the butter and chocolate mixture to the eggs and sugar, while whisking.
Add the flour, cocoa powder, ground Biscoff cookies and salt to the batter and fold them together until they're just barely combined.
1 cup (120g) all-purpose flour, 1/4 cup (25g) Dutch-process cocoa powder, 1/4 cup (30g) or 4 cookies Lotus Biscoff cookies, 1/2 tsp salt
Pour the brownie batter into the prepared pan. Place quarter sized globs of cookie butter on top and use a knife to gently swirl them into the brownie batter a little. Bake for about 45 minutes.
1/2 cup (120g) Lotus Biscoff Cookie Butter
Remove the brownies from the oven and allow them to cool in the pan for about 30-60 minutes, until they can be sliced without falling apart.