Heat oven to 350°F.
Grease 13x9x2-inch baking pan.
In large bowl, stir together butter, sugar, flour, cocoa, baking powder, eggs, milk and 1½teaspoons vanilla; beat well. Stir in nuts.
Spread batter into prepared pan.
Bake 40 minutes or until brownies begin to pull away from sides of pan.
Just before brownies are done, in heavy saucepan, melt chocolate chips with sweetened condensed milk and remaining 1½ teaspoons vanilla. Immediately spread over hot brownies.
Cool in pan on wire rack.
Refrigerate.
Cut into bars.