Line a 9x13" pan with aluminum foil, and spray with nonstick cooking spray. 

Melt butter and salt in a large pot over medium heat. Quickly stir in the marshmallows and cook until completely melted. Remove from heat. Add the vanilla extract and combine. Add the brown rice crisp cereal to the pot and mix until well-coated and combined. Add in 2/3 of the funfetti sprinkles, and gently stir to incorporate. 

Pour the mixture into the lined pan. Spray your hands or a rubber spatula with nonstick cooking spray and press down the mixture evenly into the pan. Sprinkle the remaining tablespoon of sprinkles on top. Let the treats set up and cool for about 45 minutes, then cut into 12 or 16 squares.

Enjoy! Store in an airtight container for up to 3 days.