Grease a 13x9 pan (you may also use foil or parchment)
To a large mixing bowl, add the butter. Microwave on high for 30 seconds until it begins to soften and melt
4 Tbsp salted butter
Add the vanilla extract and marshmallows to the bowl with the butter
16 Ounces mini marshmallows, 1 Tsp vanilla extract
Microwave on high for 60 seconds and stir. Continue microwaving in 30-second bursts and stirring until the marshmallows are melted (mine took 1 ½ minutes in total in a 1000W microwave)
Add both cereals and the sanding sugar to the marshmallow mixture, and stir to coat completely
Spread the coated cereal into the greased pan and press it down to form an even layer. I recommend spraying your hands well with nonstick spray, or using a greased spatula or a piece of wax paper (it is sticky!)
Top with any additional toppings if desired (optional)
Cool to room temperature (about 2 hours) or set in the refrigerator (45-60 minutes), then pop out of the pan, cut into squares, and serve!
Notes
If preferred, use all Rice Krispies and only the marshmallows from the Lucky Charms (making it more similar in texture to a traditional Rice Krispie treat). However, it’s hard to find the “only marshmallows” version and tedious to pick them out from the rest of the cereal
Swap in 64 large marshmallows in place of the mini if needed (note that they may require slightly longer to fully melt as well). You can also use flavored marshmallows such as chocolate if preferred
If you don’t have salted butter, add ½ tsp salt in to compensate
The sanding sugar is optional, but adds a fun swirl of green which is perfect for St Patrick’s Day! Feel free to top your treats with other fun festive decorations, such as sprinkles, edible glitter, or icing in coordinating colors based on your theme!
This recipe may be scaled up or down to make different size batches. Leftovers freeze well, though, so don’t worry about making extra
Fresh Rice Krispie treats are best enjoyed within 2-3 days for freshness
Store your Lucky Charms Rice Krispie treats on the counter at room temperature with a lid or other covering. Do not put them in the refrigerator beyond cooling right after cooking. Storing them there will make them dry out
Cut marshmallow cereal treats with a greased knife or use cookie cutters in seasonal shapes (like shamrocks!) to desired size
Exact nutritional values will vary based on brand of ingredients, any added toppings, and size of your cuts, so please consider this a guideline only