Step 3
In medium bowl, beat powdered sugar, 2 tablespoons butter, melted chocolate and the vanilla with electric mixer on low speed until combined. Beat in 1 tablespoon milk until blended. Beat in additional milk, 1 tablespoon at a time, until frosting is desired spreading consistency. Frost cooled brownies; sprinkle with crushed pretzels. Cut into 8 rows by 4 rows.