Adapted from Betty Crocker, Loves to Eat and Sweet Pea's Kitchen
1 cup butter
2 cups sugar
1 tablespoon vanilla
2/3 cup cocoa powder
1 cup flour
1/2 teaspoon salt
1/2 teaspoon baking powder
Peanut Butter Filling:
1/2 cup butter, at room temperature
1/2 cup creamy peanut butter
2 cups powdered sugar
2-3 teaspoons milk
2 cups semi-sweet chocolate chips
1/4 cup (1/2 stick) butter
2 tablespoons shortening
2 tablespoons heavy cream
Preheat oven to 350º. Put a long piece of non-stick foil or parchment in the bottom of a 9 x 13 inch pan, fitting so it covers the bottom of pan, the two shorter sides, plus has some overhang on each side for easy removal. If using foil, spray non covered sides of pan with nonstick spray. If using parchment, spray entire inner surface of pan with nonstick spray.
In a large microwave safe bowl, melt the 1 cup butter in the microwave. Mix in sugar, then eggs and vanilla. Sift the cocoa powder into the egg mixture, along with the salt and baking powder. Mix well. Add flour and mix till just combined. Scrape into prepared pan and smooth top.
Bake for about 25-30 minutes. Cool completely.
While brownies are cooling, mix together filling ingredients. Beat until smooth adding the extra teaspoon of milk if needed. Mixture should be spreadable. Spread filling evenly over cooled brownies. Chill for at least 30 minutes.
While filling is cooling, make ganache by melting the chocolate chips butter, shortening and cream together gently in the microwave. Stop and stir at 30 second increments, till melted and smooth. Put dollops of ganache over filling and spread gently. Return to refrigerator to set topping.