Into a bowl, sift together the sifted flour, baking powder, and salt.
Melt butter and chocolate over hot water or very low heat.
In a mixing bowl, beat eggs. Add sugar to eggs a little at a time, beating well. Blend in the chocolate and butter mixture. Stir in flour mixture, blending well. Stir in chopped walnuts and vanilla. Spread brownie batter in a greased and floured 8-inch square pan. Bake at 350° for about 25 minutes. Cool in pan and cut into squares.
Calories per bar: 182