For the Lucky Charms Rice Krispie Treats:

1. Set aside ½ cup Lucky Charms marshmallows for topping and 1 cup mini marshmallows for folding in later.
2. Use the butter wrapper to grease a 9×9-inch glass baking dish. Line with parchment paper, leaving about 2 inches of overhang on all sides for easy removal.
3. In a large pot or Dutch oven (preferably light-colored so you can see the butter browning), melt the butter over medium-low heat. Continue cooking, stirring occasionally, until the butter browns, about 8–10 minutes. Watch closely — the difference between perfectly browned and burnt is less than a minute. 
4. Once melted, the butter will separate and begin to foam heavily. Reduce the heat to low and stir frequently. As the foam subsides, you’ll see golden brown milk solids forming at the bottom (this is what we want!)
5. Remove from heat (or turn off the stove) and stir in the vanilla extract and salt. It will sizzle — keep stirring until the bubbling settles. The pan should not be overly hot before adding the marshmallows.
6. Add the marshmallows, except the 1 cup you set aside. Return to the stove and cook over low heat, stirring constantly with a rubber spatula, until just melted and smooth.
7. Stir in the Rice Krispies and the reserved cup of mini marshmallows. Mix until fully combined — the mini marshmallows should soften slightly but still hold their shape. Gently fold in the Lucky Charms cereal.
8. Immediately transfer the mixture to the prepared pan. Using a spatula, gently press it into an even layer. Avoid packing it down firmly, as this can make the bars dense.
9. Dot the top with the reserved Lucky Charms marshmallows, pressing them lightly so they adhere.
10. Let cool at room temperature for about 1 hour. Use the parchment overhang to lift the treats out, then cut into squares.
11. Store in an airtight container at room temperature for 3–5 days.