Preheat oven to 350 degrees. Line a 9 x 13" pan with parchment paper, and lightly spray with non-stick baking spray. Set aside.

In a mixing bowl, combine the brownie mix, water, oil and eggs. Mix until smooth and lump-free. Spread into prepared pan, and bake at 350 for 24-26 minutes.

While brownies are baking, mix the peanut butter filling by combining the melted butter and peanut butter. Stir until completely combined. Stir in the vanilla. Gradually mix in the powdered sugar one cup at a time. Mixture will be thick and dough-like.

Once brownies come out of the oven, let cool for about 10 minutes. While brownies are still warm, top the brownies with the peanut butter filling, and press with hands to cover completely.

For the chocolate peanut butter ganache add the chocolate chips and peanut butter into a microwave safe bowl. Heat for 1 minute on high power. Stir. Heat for another 20-30 seconds, or until all chocolate chips have melted. Pour the ganache over the peanut butter layer. Sprinkle the M&M's® Peanut Butter Candies evenly on top of the ganache. Refrigerate for at least 2 hours or overnight before cutting.