Step 1

Spray an 8x8-inch baking dish with nonstick cooking spray. Set aside.

Step 2

In a large pot over medium heat, melt butter. Add sweetened condensed milk and stir to combine. Bring the mixture to a simmer, stirring constantly to prevent burning.

Step 3

Add marshmallows, stirring frequently until melted.

Step 4

Remove the pot from heat and fold in the rice cereal with a clean rubber spatula (I like to spray the spatula with nonstick spray to prevent sticking). Stir until well coated.

Step 5

Transfer mixture into the prepared baking dish and press into an even layer.

Step 6

Allow the bars to cool to room temperature before cutting and serving.