1. Preheat oven to 375°. Line an 8x8 baking pan with parchment paper or foil leaving some hanging on each side. Set aside.

2. Mix together the melted butter and sugar until smooth.

3. Mix in the eggs and vanilla until completely combined.

4. Add in the flour and mix until everything is incorporated.

5. Press dough into pan making sure everything is even. It will be very sticky at first but once you start working with it, it will smooth out.

6. Place in preheated oven and bake for 16-19 minutes.

7. Take bars out. They should almost be done with the edges set and the middle still a little soft. Pour the marshmallows on top, try to fill every spot. Sprinkle some M&M's on top of them. Bake for 2 more minutes until marshmallows are puffy.

8. Immediately sprinkle some sprinkles on top. Don't wait too long or they will not stick.

9. Let the bars cool for about 5 minutes then pull them out by the lining and place on a wire rack or counter to finish cooling for about 20 minutes. Once cooled, cut with a wet knife and serve.

* Bars will keep for up to 5 days in an air tight container.*