Heat oven to 350F degrees. Using a spoon, stirr eggs with sugar and vanilla; add butter. Sift ground chocolate with flour, baking powder, salt. Stir into egg mixture; add nuts. Spread into greased 8- or 9-inch square pan. Bake at 350F for 20 to 30 minutes. For extra chewy brownies, use 8-inch pan and less baking time. For cake- like brownies, use 9-inch pan and longer baking. Cut into squares.