Step 1

Preheat oven to 350 degrees F. Line the bottom and sides of an 8x8-inch baking pan with aluminum foil, leaving an overhang on all sides. Set aside.

Step 2

Make the Bars: In a large bowl, whisk together the flour, oats and baking soda.

Step 3

Using an electric mixer, beat the butter, brown sugar and granulated sugar on medium speed until light and fluffy, about 2 to 3 minutes. Add the peanut butter, egg, and vanilla one after the other, mixing well after each addition. Scrape down the sides of the bowl as needed. Reduce the mixer speed to low and gradually add the dry ingredients, mixing until just combined. Do not overmix.

Step 4

Press two-thirds of the dough evenly into the prepared baking pan. Stir the M&Ms into the remaining dough. Set aside while you make the fudge ripple filling.

Step 5

Make the Fudge Ripple Filling: In a small saucepan over low heat, combine the sweetened condensed milk, butter and chocolate chips. Stir until the chocolate chips are melted and the mixture is smooth. Remove from the heat and stir in the vanilla. Pour the fudge over the bottom layer of dough.

Step 6

Mold the remaining dough containing the M&Ms into flat pieces and layer on top of the fudge filling. You won't have enough dough to make one single layer, so some of the filling will be exposed.

Step 7

Bake for 25 minutes, or until the top is lightly browned. Allow to cool completely. Lift the foil out of the pan using the overhang on the sides and cut into bars. Store in an airtight container at room temperature or in the refrigerator for up to 1 week.