Peanut Butter Swirl Brownies

Bahan-bahan (16 porsi)

• ½ cup (1 stick) unsalted butter
• 1 cup granulated white sugar
• 2 large eggs
• 1 teaspoon vanilla extract
• 1 cup all purpose flour
• ½ teaspoon salt
• 2 ounces unsweetened chocolate, (melted and cooled)
• ⅓ cup peanut butter ((chunky or creamy))
• ¼ cup mini semisweet chocolate chips