Rub a little butter into the bottom of an 8-inch square baking pan, as glue. Line with two lengths of parchment paper, crisscrossed. In a heavy saucepan melt 4 ounces (1 stick) unsalted butter and 4 ounces unsweetened chocolate. Stir in one cup sugar and 1 teaspoon vanilla. Beat in 2 eggs, ½ cup sifted cake flour and a pinch of salt. Pour into the pan and bake at 350F for 18-20 minutes, until a toothpick inserted in the center comes out speckled with crumbs, not batter. Cool on a rack for a few minutes, then lift out the brownie by grasping the free ends of the parchment paper. When cool trim away the firm edges. These scraps are the cook’s reward. Enjoy them while slicing the brownie into 16 small but effective squares.