PREHEAT oven to 350 degrees. Lightly grease 8x8 or 9x9 pan. If using glass, reduce to 325 & bake 5-10 minutes less.
WHISK together cocoa, sugar, salt, baking powder, and flour. Add nuts and chocolate chips, if desired.
STIR in eggs, oil (or melted butter) & water (or coffee), mixing until evenly blended. Spoon the mixture into pan, smoothing the top.
BAKE for 45 minutes (for 8x8 pan) or 35 minutes (for 9x9 pan), until a toothpick inserted into the center comes out with just a few moist crumbs.
COOL on a rack for 1 hour before slicing.
