Step 1: In a medium bowl, combine the graham cracker crumbs, melted unsalted butter, and granulated sugar. Mix until thoroughly combined. Press this mixture firmly into the bottom and up the sides of a 9-inch pie dish. Refrigerate the crust to chill while preparing the filling.
Step 2: In a large mixing bowl, beat the softened cream cheese with an electric mixer until it is smooth and lump-free.
Step 3: Gradually add the powdered sugar to the beaten cream cheese, mixing until fully incorporated and the mixture is light and creamy. Scrape down the sides of the bowl as needed.
Step 4: In a separate, chilled bowl, pour the heavy whipping cream. Using an electric mixer, beat on high speed until stiff peaks form.
Step 5: Gently fold the whipped cream into the cream cheese and powdered sugar mixture using a spatula, being careful not to deflate the cream.
Step 6: To the mousse mixture, add the smooth peanut butter and melted chocolate. Stir gently until these additions are evenly distributed and fully incorporated.
Step 7: Fold in 1 cup of M&M’s, reserving the remaining ½ cup for garnishing the top of the pie.
Step 8: Carefully pour the prepared chocolate mousse filling into the chilled graham cracker crust. Use a spatula to spread it evenly, smoothing the top.
Step 9: Place the pie back into the refrigerator to chill for at least 4 hours, or preferably overnight, to allow the mousse to set completely.
Step 10: Once the pie is fully set, sprinkle the reserved ½ cup of M&M’s evenly over the top.
Step 11: For an optional extra touch, drizzle any leftover melted chocolate over the top of the pie in a decorative pattern.
Step 12: Slice your beautifully set No Bake Chocolate Mousse Pie and serve chilled. Enjoy!