Preheat the oven to 350 degrees F. Grease an 8-by-8-by-2-inch pan.
Melt the chocolate and shortening together in a small saucepan. Stir the sugar into the well-beaten eggs in a large bowl. Combine the chocolate and the egg mixtures in the bowl.
Add the baking powder and salt to flour and sift. Add the flour mixture to the chocolate mixture; add the vanilla and nuts, if using. Stir to combine.
Spread the dough evenly in the pan. Bake 25 to 30 minutes. Cool 30 minutes, cut into squares and enjoy.
Recipe from Fine Sweet Shoppe, Washington DC