Special equipment: a 2-inch round cookie cutter, a piping bag or resealable plastic bag and a kitchen torch
Prepare the brownie according to the package directions. Allow to cool completely; do not cut the brownie into pieces. Place the cooled slab of brownie on a flat surface. Using a 2-inch round cookie cutter, cut out 18 brownie circles; reserve the brownie trimmings for another use. Transfer the brownie circles to a serving platter.
Put the marshmallow creme into a piping bag or a resealable plastic bag with one corner snipped.
Working quickly, scoop vanilla ice cream onto each brownie circle. Quickly pipe marshmallow creme in a swirl shape around the brownie and ice cream so that they are completely covered. Use a kitchen torch to carefully heat the marshmallow domes until just browned. Serve immediately or store in the freezer in an airtight container for up to 1 week.