Irresistible Brownies

3/4 c. butter
2 c. sugar
1 1/2 c. flour
1/2 c. cocoa powder
1/2 t. baking powder
1/4 t. salt
4 eggs
2 t. vanilla
2 c. chocolate chips
1/2 c. chopped nuts (optional)

Preheat oven to 350 degrees. Grease a 9x13 pan. In a medium saucepan over low heat, melt butter. Remove from heat and add remaining ingredients, reserving 1/2 cup of chocolate chips. Pour into baking pan. Sprinkle remaining chocolate chips on top. Bake 30 to 35 minutes.