To prepare TAN BROWNIES:, place butter and sugar in a medium bowl; beat with the mixer on low speed until fluffy. Beat in 2 eggs and 1 tsp. vanilla. Gradually add 1 cup flour, baking powder, and cinnamon; stir well. Add to sugar mixture along with nuts; beating just until combined. Spoon into a greased 13x9" baking pan. Spread evenly and bake for 15 mins.
To prepare BLACK BROWNIES: melt chocolate and butter in a medium saucepan until smooth. Add sugar until well combined. Add eggs, vanilla, and Guinness;whisk until combined. Add flour and combine. Pour mixture over baked TAN brownies.
Bake on center rack of oven for 25-30 minutes until knife inserted comes out almost clean.Cool in the pan. Cut into squares and serve with ice cream