Lightly spray x 9x13 pan or line with with aluminum foil. You can use a smaller pan if you want thicker treats.
Melt butter in a very large pot on low heat.
Open one bag of marshmallows and reserve 2 cups of mini marshmallows. Set these aside. These will be stirred in at the very end.
When butter is melted, add the remaining marshmallows (1 whole bag, and what's left of the second bag). Stir with a rubber spatula or a wooden spoon until melted.
Remove from heat. Stir in vanilla extract and salt.
Stir in remaining 2 cups mini marshmallows, rice krispies, 1/2 cup white chocolate, and sprinkles.
Spread in pan (use a piece of saran wrap lightly sprayed with cooking spray) and press into the pan.
Melt remaining 1/2 cup of white chocolate chips in microwave. I microwave in 30-second intervals stirring in between each addition to make sure they don't burn. Drizzle on bars.
Let sit for 10 minutes. Cut into squares and enjoy.