Melt the 5 tablespoons of unsalted butter in a large saucepan over low heat until completely melted and bubbly. Keep an eye on it to ensure it doesn’t brown.
Add 1 (16-ounce) bag of miniature marshmallows (reserve 1 cup for later) to the melted butter. Stir continuously until the marshmallows are completely melted and smooth, about 2-3 minutes.
Remove the saucepan from heat. Stir in 1 teaspoon of vanilla extract and 1/4 teaspoon of salt to the melted marshmallow mixture.
Gradually add 6 cups of Rice Krispies cereal to the marshmallow mixture, stirring gently but thoroughly to coat the cereal.
Fold in the reserved 1 cup of miniature marshmallows and 1/3 cup of white chocolate chips.
Prepare your 9x13-inch baking pan by greasing it with 1/4 teaspoon of vegetable oil or lining it with parchment paper. Pour in the mixture and press it down firmly into an even layer.
If desired, sprinkle colorful sprinkles on top before the mixture sets.
Allow the Rice Krispie Treats to cool for at least 30 minutes at room temperature. Once set, cut into squares or rectangles and serve!
