In a large microwave safe bowl, combine the butter with chocolate chips. Heat for one minute on high. Stir and microwave for another 30 seconds. You may need to stir and heat for one more round of 30 seconds until fully melted. Add sugar, flour, eggs and salt. Stirring until well blended. Fold in peanut butter morsels
Lightly grease mini muffin pan with baking spray. Drop dough by large tablespoons until evenly divided into pan.
Bake in a 375 degree oven for 12-14 minutes. Remove and cool in pan 5 minutes, then cool completely on wire rack.
For the frosting, beat butter and powdered sugar for 3-4 minutes until smooth and fluffy. Bean in milk and peanut butter until creamy and desired consistency. Pipe frosting onto cooled brownies and top with a mini Reese's.