Heat butter in a medium-sized pot over low heat until melted
Add vanilla extract and salt, and mix until blended.
Add marshmallows and stir until mostly all are melted.
Add a very tiny amount (tip of a knife) of food coloring and mix until blended. Keep adding until you get your desired color. Blend thoroughly until the color is solid and there are no color streaks left.
Add the marshmallow mixture to the rice cereal in a large mixing bowl and mix thoroughly.
Spray a 9" x 13" baking pan with cooking spray. Add marshmallow-cereal mixture and spread. Do not press down too hard. To further prevent sticking, also spray the spreading utensil prior to spreading in the pan.
Cut Rice Krispie treats into 18 servings.
Melt the white chocolate candy melts in the top of a double boiler.
Dip each treat into the white chocolate and top each with sprinkles. Add sprinkles right after dipping, to ensure the sprinkles will stick before the chocolate re-hardens.
Notes
*Make sure to use low heat when melting butter and marshmallows. Keep the heat as low as possible to prevent them from becoming too hard in the end.*Imitation vanilla can be used instead of pure vanilla extract.*When melting the marshmallows, keep an eye on the pan the entire time to ensure the mixture doesn't get too hot and burn.*Gel food coloring gives a better color result than liquid food coloring drops.*Work quickly with spreading the cereal mixture and cutting into squares. The mixture becomes very sticky as it cools and also becomes harder to work with.*A double boiler is a pan with water heated to a low boil, with a glass bowl placed directly on top. This helps the item in the bowl melt at a more even and consistent temperature and can prevent it from breaking or separating.