Preheat your oven to 350°F. Grease and line a 9x13 inch baking pan with parchment paper, ensuring the paper hangs over the edges for easy removal.

In a large mixing bowl, combine the melted butter and granulated sugar. Using an electric mixer, beat on medium speed until well blended. Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.

In a separate bowl, whisk together the all-purpose flour, cocoa powder, baking powder, and salt. Gradually add the dry mixture to the wet ingredients, mixing just until combined and smooth.

Pour the batter into the prepared baking pan, spreading it evenly. Bake for 20-25 minutes or until a toothpick inserted into the center comes out with a few moist crumbs. Allow the brownies to cool completely in the pan on a wire rack.

Once cooled, lift the brownies out of the pan using the parchment paper. Use a serrated knife to cut the brownies into equal squares or rectangles, depending on the desired sandwich size.

Place a scoop of slightly softened vanilla ice cream on one brownie piece. Top with another brownie piece and gently press down. Repeat with remaining brownies and ice cream.

Wrap each sandwich in plastic wrap and freeze for at least 1 hour or until the ice cream is firm. Serve immediately after removing from the freezer for the best taste and texture.

Individually wrap any leftover sandwiches in plastic wrap and store in an airtight container in the freezer for up to 2 weeks.