Preheat oven per brownie mix directions; parchment-line two baking sheets.
Prepare brownie batter per package; fold in optional cocoa and chips.
Drop tablespoon scoops 1.5 inches apart into small rounds.
Bake 8–10 minutes until edges set but centers remain soft; cool on sheet 5 minutes.
Cool cookies completely on rack to avoid melting ice cream quickly.
Sandwich a small ice cream scoop between cookies; press gently. Roll edges in optional powdered sugar.
Freeze sandwiches on tray 30–60 minutes to firm before serving.