In a small heavy saucepan melt the chocolate and the butter over low heat, stirring until the mixture is smooth, and let the mixture cool completely. Into a bowl sift together the flour, the baking powder, and a pinch of salt. In a large bowl with an electric mixer beat the eggs, add the sugar, a little at a time, beating, and beat the mixture at high speed for 3 minutes, or until it is thick and pale. Stir in the chocolate mixture and the vanilla, add the flour mixture, stirring until the mixture is blended well, and stir in the walnuts. Pour the batter into a buttered and floured 8-inch-square baking pan, smoothing the top, and bake it in the middle of a preheated 350° F. oven for 25 to 30 minutes, or until it pulls away slightly from the sides of the pan and a wooden pick inserted in the center comes out with crumbs adhering to it. Let the brownies cool completely before cutting them into squares. cook 029