Preheat oven to 350 degrees F. Grease and flour a 9 inch square baking pan.
Melt unsweetened chocolate either in a microwave or in a double broiler. Be real careful to NOT scorch chocolate. Cool chocolate to room temperature.
In a large bowl, beat butter and sugar until light and fluffy. Individually add eggs, beating after each addition. Add vanilla, mix until incorporated.
In a small bowl, sift together flour, baking powder, and salt. Add flour mixture to butter mixture. Mix until just blended.
Divide batter between two bowls. Whisk melted chocolate into 1 batter and peanut butter into other batter. Stir in peanut butter chips into chocolate batter. Stir in chocolate chips into peanut butter batter.
Spread peanut batter onto prepared baking pan. Carefully spread chocolate batter on top of peanut butter batter. Bake for 35 to 40 minutes or until cake tester inserted into center of brownies comes out clean.