Best Brownies in Great Valley

Ah, yes, the legendary Best Brownies of Great Valley. Looks like I'm the first to post this one. :) I won't include the story, but if someone else wants to add it to my post, I'm OK with that.

1-1/4 cups butter
3/4 cup unsweetened cocoa
1-1/3 cups flour
1 teaspoon salt
1 teaspoon baking powder
4 eggs
2 cups sugar
1 teaspoon vanilla
12 ounces chocolate chips
1 cup chopped pecans or walnuts

Preheat oven to 350 degrees.

Make the following mixtures in three separate bowls:
1) Cocoa Mixture-In the largest bowl, melt butter then stir in cocoa.
2) Flour Mixture-Mix together flour, salt, and baking powder.
3) Egg Mixture-Mix together eggs, sugar, and vanilla.

Alternately add the dry mixture and the egg mixture to the cocoa mixture. Stir just until smooth. Add chocolate chips and chopped nuts. Bake in a greased 9x13" pan for 30 minutes. *Put into the refrigerator immediately.

*The keys to success are to not overcook (they will not look completely done at first), and to let them cool completely before serving.

A couple of notes..
-I made this recipe twice over the last year or so and they were really bitter - I was using regular cocoa and semi-sweet chocolate chips. So unless you want really bitter brownies, it looks like "dark chocolate" doesn't work. I used milk chips this time and they turned out perfectly.
-Also, normally I do not like nuts in things, but I love nuts in brownies. I know I'm a little strange, but you're all used to me.
-Since moving to Arizona (both in Phoenix and where we are now), brownies and bar cookies take much longer to cook than they did back east. Sometimes up to 30 minutes longer. Anyone know why this is? I haven't taken the time to experiment with different temperatures and baking times.