Line a 9x9 square baking dish with parchment paper. Spray with non-stick spray.
In a heavy-bottomed saucepan, melt butter over medium heat.
6 tbsp. salted butter
Add marshmallows and stir continuously until completely melted. Turn off the heat and add vanilla.
16 oz. mini marshmallows, 1 tsp. vanilla extract
Pour cereal into marshmallow mixture and quickly mix with a rubber spatula until fully coated.
8 cups (10.5 oz. box) Lucky Charms cereal
Lightly press mixture evenly into pan using rubber spatula or butter your fingers to press into the pan.
Allow bars to cool for 30 minutes before cutting into squares.
