Preheat your oven to 350°F.

Butter a 9-by-13-inch metal baking dish and line it with parchment paper.

In a small saucepan, melt the butter over low heat.

Remove from heat and add the chocolate, stirring until melted. If needed, reheat for 10 seconds.

Set the chocolate mixture aside to cool.

Sift the flour, cocoa powder, and a pinch of espresso powder into a bowl and set aside.

In a medium bowl, combine eggs, sugars, salt, and vanilla. Beat on high speed until thick and pale, about 4-5 minutes.

Fold the cooled chocolate mixture into the egg mixture with a spatula.

Gently fold in the flour mixture, keeping the batter airy.

Pour half the batter into the baking dish, spreading evenly.

Layer Thin Mint cookies over the batter.

Pour the remaining batter over the cookies and smooth the top.

Bake for 25-30 minutes, until the top looks cracked and feels soft.

Let cool completely on a wire rack.

Cut into 12 squares or your desired size with a sharp knife.