Heat oven to 350 degrees. Grease a square 8×8 inch baking pan. Melt chocolate and shortening over low heat. Beat in sugar and eggs. Stir in flour, baking powder, and salt, until blended. Mix in nuts. Spread in pan. Bake 30 to 35 minutes, or until top has a dull crust and a slight imprint remains when touched lightly. Cool slightly and cut in squares. May be frosted if desired.