Prepare an 8x8 inch pan and line with parchment paper. Set aside.
In a medium sized saucepan over low heat melt 2 cups peanut butter chips with one cup of the 1 (14-ounce) can sweetened condensed milk about 3-4 minutes. Spread evenly in your prepared pan.
In a small saucepan over low heat, melt ¼ cup semi-sweet chocolate chips with remaining sweet and condensed milk. Remove from heat, add 1 teaspoon vanilla and 2 tablespoons butter and stir until smooth.
Drop the chocolate mixture evenly over the peanut butter fudge. Use a knife and create a swirl through the top of the fudge. Chill for 3 hours or until firm