Prepare the pan by greasing an 8x8-inch baking pan with butter to prevent sticking.

In a large mixing bowl, combine the Rice Krispies cereal and cinnamon thoroughly.

Melt 4 tablespoons of salted butter over low heat in a large pot. Stir frequently.

Add 4 cups of mini marshmallows to the pot and stir until almost melted with some lumps remaining.

Remove from heat and fold in the Rice Krispies and cinnamon mixture until well coated.

Transfer the mixture into the prepared baking pan and press down evenly.

Mix together the cinnamon sugar and sprinkle it over the pressed treats evenly.

Allow the treats to cool at room temperature for about 30 minutes before slicing.