Prepare the pan by spraying an 8×8-inch pan with non-stick spray, line it with foil or parchment, and sprinkle 3 tablespoons of cinnamon sugar evenly across the surface.

In a large microwave-safe bowl, combine 4 tablespoons of butter, 1/4 teaspoon of sea salt, and 8 cups of mini marshmallows. Microwave in 30-second intervals until melted and smooth (1.5 to 2 minutes total).

Stir in 1 teaspoon of vanilla extract until fully combined, creating a glossy mixture.

Fold in 3 cups of Cinnamon Sugar Rice Krispies cereal and 3 cups of regular Rice Krispies cereal using a spatula until just combined.

Gently fold in 1 cup of additional mini marshmallows until warmed through, retaining their shape.

Transfer the mixture into your prepared pan and press it down firmly to avoid crumbling.

Sprinkle the remaining cinnamon sugar over the top and gently press it into the surface to adhere.

Allow the mixture to set at room temperature for at least 30 minutes until firm.