Preheat the oven to 325°F. Line 18 muffin tins with liners.
Sift together flour and salt. Set aside.
Melt 1/4 cup of the chocolate chips with the butter in the microwave, stir to mix. This should take 30-45 seconds, depending on the wattage of your microwave.
In a large mixing bowl, beat together the egg and sugar. Add the melted chocolate, butter and vanilla, then slowly incorporate the sifted flour until just mixed. Fold in remaining chocolate chips by hand.
Fill each muffin well 2/3 full. Bake for 20-25 minutes or until tops crack. Remove and cool.
Peanut Butter Frosting:
Meanwhile, in a medium mixing bowl using an electric beater beat together the powdered sugar, butter, peanut butter, and milk.
Pipe or spread onto the tops of cooled brownies. Decorate as desired.
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