Several hours before you want to serve the brownies, make the fudge and chill in the refrigerator.
Preheat the oven to 325°F. Grease a 9x13 pan with butter or line with parchment.
Melt the butter in a medium saucepan over medium-high heat. Add the chocolate chips and stir until melted. Remove from the heat. Add the sugar, vanilla, and stir until smooth.
Whisk in the eggs. Add the flour and salt. Stir until well combined. Stir in 1 cup of peanut butter fudge chunks. Pour into a well-greased or parchment-lined pan. Top with remaining pieces of peanut butter fudge.
Bake for 30-34 minutes, until a toothpick inserted in the center of the brownies, comes out with moist crumbs.
COOK’S NOTE: These brownies will keep nicely in an airtight container at room temperature for several days. Alternatively, they can be wrapped airtight and frozen for up to 3 months. Thaw at room temperature before eating.