2 Melt butter in medium saucepan over low heat. Add cups sugar and cocoa; stir to blend. Remove from heat. Stir in eggs and vanilla. Stir together flour, salt and baking soda; stir into chocolate mixture. Stir in 2/3 cup mini peanut butter cups; spread mixture in prepared pan
Combine peanut butter and remaining 2 tablespoons sugar. Drop by tablespoons onto chocolate batter. Swirl with metal spatula or knife for marbled effect
Bake 25 to 30 minutes or until brownie starts to pull from edges of pan and is set. Cool 45 minutes; sprinkle remaining 2/3 cup peanut butter cups over surface, pressing in slightly. Cool completely in pan on wire rack. Cut into squares or triangles. About 36 brownies.