Start by placing mini M&Ms in the freezer to prevent melting while you prepare the treat base.

Line a 9-inch by 13-inch baking dish with parchment paper to prevent sticking.

In a large pot, melt together butter and cookie butter over medium heat until smooth and completely liquid.

Remove from heat and let cool for 1-2 minutes. Add one bag of mini marshmallows, stirring until fully melted.

After the first bag is melted, add the second bag and mix in the crisp rice cereal until combined.

Gently fold in half of the mini M&Ms, being cautious not to overmix to keep them whole.

Transfer the mixture into the prepared baking pan. Using a spatula or greased fingers, press down evenly.

Sprinkle the remaining M&Ms on top and gently press to embed them into the treat mixture.

Allow the bars to cool for at least 2 hours before cutting them into 12 squares for serving.