Brown butter (see directions in post for more help). Make sure to scrape the bottom of the pot to get all the brown flecks!
Cream butter and sugars until well combined.
Add eggs and vanilla, mix until there are no lumps.
Sift together dry ingredients and add to mixture. Mix on low, scraping sides of bowl, until well combined.
Using a spatula or spoon, fold in Fruity Pebbles crunch mixture and marshmallows.
Refrigerate cookie dough for 45 mins-3 hours (cookie dough must be cold)
Preheat oven to 375 degrees.
Scoop cookie dough into 1.5-2 oz mounds and place 2-3 inches apart on a baking sheet lined with parchment paper or silicone baking mats.
Bake cookies for 9-11 minutes, or once edges have set and the tops are starting to brown.
Allow cookies to cool for 20-30 minutes on warm sheet before removing.