Line an 8x8- or 9x9-inch baking dish with foil (I used an 8x8 for extra thick treats). Generously coat with nonstick spray and set aside.

Place the butter in a large skillet or pot over medium heat. Once the butter is melted, add the Champagne, stir, and let it gently simmer for 1 minute. Add half of the marshmallows, vanilla extract, and kosher salt. Stir until the marshmallows are completely melted, about 4 minutes.

Remove the skillet from the heat and add the cereal. Fold gently to combine. Fold in the remaining marshmallows (plus extra if you so desire). The marshmallows will not melt completely, which is the entire delicious idea. Lightly press into the prepared baking dish. If the mixture is difficult to spread, I find lightly coating a sheet of plastic wrap with nonstick spray, and then laying it over the top to press with my fingers, works nicely. Let cool completely, and then slice and serve. Or eat it as a sticky mess right out of the pan. No judgment.