Combine the flour, salt and baking powder; set aside. In a saucepan, melt butter and brown sugar. Remove from the heat and stir in maple syrup. Cool mixture to lukewarm. Beat in eggs and flavoring. Stir in flour mixture and nuts.
Pour into a greased 8-in. square baking pan. Bake at 350° for 25 minutes or until edges pull away from the sides of the pan. Cool on a wire rack.
For glaze, combine sugar, syrup and enough milk to achieve a pourable consistency. Drizzle over brownies.