📖 Instructions

1. Prepare your baking pan: Line an 8x8 inch (20x20 cm) baking pan with parchment paper, allowing some overhang on the sides. This creates 'handles' to easily lift the squares out later. A little cooking spray underneath the parchment can help it stick to the pan.
2. Make the cookie crust: Take your chocolate sandwich cookies (about 36 cookies, or one standard package) and crush them into fine crumbs. You can do this by pulsing them in a food processor or by placing them in a Ziploc bag and crushing them with a rolling pin or the bottom of a heavy glass. You'll want about 2 cups of crumbs.
3. Combine crust ingredients: In a medium bowl, mix the cookie crumbs with the melted unsalted butter. Stir until the crumbs are evenly moistened and resemble wet sand. It should hold together when you squeeze a little bit.
4. Press the crust: Firmly press the cookie mixture into the bottom of your prepared baking pan. Use the back of a spoon or your clean hands to create an even, compact layer. Place the pan in the refrigerator while you prepare the mint filling.
5. Prepare the mint filling: In a large mixing bowl, using an electric mixer (or a sturdy whisk and some arm strength!), beat the softened unsalted butter until it's light and fluffy, about 2-3 minutes. Make sure your butter is truly soft, not melted, for the best texture.
6. Add powdered sugar: Gradually add the powdered sugar, one cup at a time, beating well after each addition until fully incorporated. The mixture will become very thick and crumbly at first, but keep going.
7. Incorporate cream and flavor: Pour in the heavy cream, mint extract, and a few drops of green food coloring (if desired, to get that classic mint green hue). Start with 1/2 teaspoon of mint extract and taste it – mint extract can be quite strong! Beat on medium speed until the mixture is smooth, creamy, and a lovely pale green. If it's too thick, add another tablespoon of cream; if it's too thin, a bit more powdered sugar can help.
8. Spread the mint layer: Remove the chilled crust from the refrigerator. Carefully spread the mint filling evenly over the cookie crust using an offset spatula or the back of a spoon. Try to get it as smooth as possible. Return the pan to the refrigerator to chill for at least 30-45 minutes while you make the topping.
9. Make the chocolate topping: In a microwave-safe bowl, combine the semi-sweet chocolate chips and the unsalted butter (or coconut oil). Microwave in 30-second intervals, stirring well after each, until the chocolate is completely melted and smooth. Be careful not to overheat it, as chocolate can seize up.
10. Pour and spread topping: Take the partially chilled squares out of the fridge. Pour the melted chocolate topping over the mint layer and quickly spread it evenly to the edges. Work relatively fast here, as the cold mint layer will start to set the chocolate quickly.
11. Chill thoroughly: Return the pan to the refrigerator and chill for at least 2 hours, or until the chocolate topping is completely set and firm. For the cleanest cuts, I often let it chill for 3-4 hours, or even overnight.
12. Cut and serve: Once fully chilled, use the parchment paper overhang to lift the entire slab of squares out of the pan and onto a cutting board. Use a sharp knife, wiping it clean between each cut for the neatest edges. Cut into 16 or 25 squares, depending on your preferred size. Serve cold and enjoy that wonderful cool bite!