Line and spray a 9x13 inch baking pan with parchment paper. Set aside.

In a large saucepan, melt the butter over medium-low heat. Cook the butter, swirling occasionally, until it turns a golden brown color and gives off a nutty aroma, about 5-7 minutes. Be careful not to let it burn.

Once the butter is browned, add the marshmallows to the saucepan. Stir constantly until the marshmallows are completely melted and well combined with the brown butter. Add the vanilla and mix.

Remove the saucepan from the heat and quickly stir in the crispy rice cereal until it's evenly coated with the marshmallow mixture. Let it sit for 1 minute, and then gently fold in the chocolate chips, sprinkles, and mini marshmallows. Carefully fold it and be careful not to over work it and cause the sprinkles to bleed their color.

Transfer the mixture to the prepped greased 9x13-inch baking dish. Use a greased spatula or your hands (make sure they're greased too to prevent sticking) to press the mixture firmly and evenly into the dish. Garnish with a few more sprinkles, marshmallows, and white chocolate chips.

Allow the treats to cool completely at room temperature before cutting into squares.