Line a 9x13-inch baking pan with foil and spray with baking spray. Set aside.

In a large pot on the stovetop, over medium heat, melt the butter. Add the entire bag (or 8 cups) of marshmallows to the melted butter and continue cooking over medium heat. Stir occasionally until the marshmallows have melted. Remove the pot from the stove.

Stir in the white chocolate chips, salt and vanilla extract into the marshmallow mixture. Once the white chocolate is mostly melted, fold in the Chex cereal, one cup at a time. Fold in the fruity marshmallows.

Pour the mixture into the prepared pan, gently pressing the mixture into the pan. Top with sprinkles.

Allow treats to cool and set in the pan completely before cutting into desired sized squares (2-3 hours).