In a large stovetop pan, wok, or skillet melt butter and marshmallows over medium heat until blended and smooth

Whisk in vanilla extract and peanut butter until well incorporated, remove from heat.

Gently fold in honey nut cheerios with large spatula until evenly coated with marshmallow mixture

Sprinkle in M&M Candies and fold as before until just combined

Firmly press bars onto a greased 11x17 cookie sheet and let cool, slice into square bars and serve!