Prepare the brownie mix in a 9x9 inch pan, according to the box directions.

Allow the brownies to cool completely.

For the frosting, beat the butter and powdered sugar.

Add the vanilla, and continue to mix.

Alternate adding the gel food coloring and small amounts of milk until the frosting forms and is the shade of green you want.

Frost the top of the cooled brownies. Top with green M&Ms and heart sprinkles.