Mom's Cocoa Brownies

This recipe isn't actually mom's, but she makes them fantastically and I got the recipe from her, so the credit goes to mom. We had these in place of birthday cake for my party yesterday.

3/4 c butter, softened
3 eggs
1 1/2 t vanilla
2/3 c cocoa powder
1 1/4 c flour
1 c sugar
3/4 c packed light brown sugar
1/2 c walnuts, chopped (optional)
1 t baking powder
1/4 t salt

1. Preheat oven to 350 degrees F.
2. Combine all ingredients and pour into 9x13 greased pan.
3. Bake 20-25 minutes, until brownies spring back when lightly touched. Do not over bake (then they're no longer gooey!).