Mix the chocolate brownies according to package directions (i.e., mix package with 1/2 cup oil, 1/4 c water, and 2 eggs for 50 strokes).

Fold in the cup of chopped pecans into the batter.

Spread the batter mixture in a greased pan and bake for 25 minutes.

Remove from oven and sprinkle the miniature marshmallows over the hot brownies so the melt a bit. Cool.

In a heavy saucepan, melt the chocolate, milk, and butter together until combined (be sure to stir constantly).

Remove chocolate mixture from the heat and add the vanilla.

Add the powdered sugar a little at a time, mixing with a hand mixer on low speed, until the frosting is the desired consistency for spreading.

Spread over brownies with marshmallows.

Cool and cut into bars.