Creating these Brownie Ice Cream Sandwiches is a simple process. Follow these steps to make this delightful dessert:

1. Preheat Oven: Begin by preheating your oven to 350°F (175°C) and greasing a 9×13-inch baking pan.
2. Mix Butter and Sugars: In a large bowl, combine the melted butter, granulated sugar, and brown sugar. Mix until well combined.
3. Add Eggs and Vanilla: Beat in the eggs one at a time, then stir in the vanilla extract until the mixture is smooth.
4. Combine Dry Ingredients: In another bowl, whisk together the flour, cocoa powder, baking powder, and salt.
5. Combine Mixtures: Gradually add the dry mixture to the wet mixture, stirring until just combined. If desired, fold in chocolate chips or nuts.
6. Pour into Pan: Spread the brownie batter evenly into the prepared baking pan.
7. Bake: Place in the preheated oven and bake for 25-30 minutes, or until a toothpick inserted in the center comes out mostly clean (a few crumbs are fine).
8. Cool: Remove from oven and let cool in the pan for about 15-20 minutes before transferring to a wire rack to cool completely.
9. Cut into Squares: Once cooled, cut the brownies into even squares, about 2×2 inches.
10. Assemble Sandwiches: Take one brownie square, scoop a generous amount of softened ice cream, and sandwich it with another brownie square on top. Press gently to adhere.