Line a 9x13-inch baking pan with parchment paper. Set aside until ready to use. Melt unsalted Irish butter in a large stock pot over low heat. Then, pour in the mini marshmallows. Stir constantly with a silicone spatula until the marshmallows have melted and the mixture is smooth and well combined.
Remove from the heat and pour in the Lucky Charms Cereal. Quickly and carefully stir with a silicone spatula to coat all of the cereal with the marshmallow mixture, taking care not to crush the cereal.
Transfer the mixture to the prepared pan. Spray your hands with non-stick cooking spray and gently press the mixture evenly into the pan. If you press too hard, you'll end up with hard marshmallow treats. Allow to cool for about 30 minutes before topping.
After the marshmallow treats have cooled, melt bright white and green candy melts separately in the microwave according to the package directions. Pour the white candy melts over the top of the Lucky Charms treats. Then, use a silicone spatula to smooth into an even layer.
Next, drizzle the green candy melts over the white.
Use a thin wooden skewer or knife to swirl the white and green together.3 Top with extra Lucky Charms Marshmallows and gold sanding sugar.
Allow the candy melts to harden completely, for about an hour. Then, remove from the pan and cut into squares.
Yield 12 servings
Tips/Notes
You can substitute regular unsalted butter.
I was able to find a bag of Lucky Charms Just Marshmallows at Target. If you can't find them, I recommend buying a second box of Lucky Charms and picking the marshmallows out to decorate the top with.
If the candy melts begin to harden too quickly while swirling or topping with extra marshmallow and sanding sugar, pop the pan in a 300°F oven for a few minutes to melt again.