Heat your oven to a high broil and line a baking sheet with parchment paper.
Place the large marshmallows on the baking sheet and place under the broiler until browned (it only takes about 30 seconds so keep a close eye on them)
Take the pan out of the oven, turn the marshmallows over and broil the other side until golden. Remove from the oven and set the marshmallows aside.
Making the Browned Butter Rice Krispie Treats
Prepare a 9x13 baking dish. You can grease the pan with butter or use parchment paper if you're planning to lift the rice krispies out of the pan before slicing
Slice the butter and add it to a large pot over medium heat. Allow it to melt completely then continue stirring until the solids in the butter turn brown. You may notice some foam and that's okay. Once browned, remove from the heat.
Add in the large toasted marshmallows (or un-toasted if you chose not to toast), the marshmallow creme, vanilla, and salt. Stir together until everything is melted.
Add in the rice krispie cereal and stir everything together. Once combined, stir in 4 cups of the mini marshmallows. (you should just have a few left over for topping the treats)
Add the rice krispie mixture to the prepared dish and press gently to even them out. (Don't press too hard and compact them or they will become too dense)
Sprinkle the remaining mini marshmallows over the top and press them gently down so they stick. Allow the treats to set for about 30-60 minutes before slicing.
Store covered, at room temperature for up to 7 days...if they last that long!