Line your 8x8 pan with a piece of parchment paper set to the side until needed.

In a large pot or Dutch oven add your butter and cook on medium heat. Melt butter and then reduce to medium-low heat. Swirl the pan and scrap the bottom of the pan with a wooden spoon every once in a while.

The melted butter will begin to foam and there will be a nutty aroma. You'll start to see small brown particles on the bottom of the pan. Don't walk away! Once the brown specks turn a bit browner you can take it off the heat.

Add in the marshmallows. Stir the marshmallows until it melts and then add in the vanilla extract.

Stir in the cereal until the marshmallows completely coat the cereal and then add the remaining marshmallows.

Pour the rice crispy mixture into the prepared pan and then slightly press the rice crispy down with a buttered or rubber spatula with nonstick cooking spray to create an even layer.

Let the brown butter rice crispy treats set for at least one hour before cutting.