Preheat oven to 350 degrees F. In a microwave safe bowl, melt chocolate chips, add eggnog to melted chocolate, microwave for 30 seconds.
Cream together butter and brown sugar, beat in the eggs and rum extract.
Add the melted chocolate eggnog mixture.
Fold in baking powder, salt and flour, mix until just incorporated.
Pour batter into a lightly greased 8-inch square pan.
Bake for 25-30 minutes, or until toothpick comes out clean.
Whisk together the powdered sugar, eggnog and nutmeg, if the glaze is too thick add a little more eggnog.
Pour over cooled brownies.