Start by cleaning the mussels thoroughly; scrub their shells under cold water while removing the beard with your fingers. Once cleaned, place the mussels in a large pot and cover them. Cook over medium-low heat for about 5-7 minutes, or until the shells open up. Discard any that remain closed. Allow the mussels to cool slightly, then gently separate the shells, keeping the halves for stuffing.

In a saucepan over medium heat, melt about 2 tablespoons of butter and then add 2 minced garlic cloves. Sauté until the garlic is tender and fragrant, about 1-2 minutes. Stir in approximately 2 tablespoons of breadcrumbs and gradually pour in 1 cup of milk while whisking constantly. Continue to stir until the mixture thickens to a creamy consistency, which should take 3-5 minutes. Season with salt to enhance the flavor, then set the sauce aside.

Arrange the cleaned mussel halves on a baking tray that has been lined with parchment paper for easy cleanup. Using a teaspoon, carefully fill each shell with the creamy garlic-bechamel sauce prepared in the previous step. Be generous but mindful not to overfill. Sprinkle a thin layer of grated quick-melt cheese on top of each stuffed mussel to create a deliciously gooey topping.

Preheat your oven to 355°F (180°C). Once the oven reaches the right temperature, place the baking tray with the stuffed mussels inside and bake for 10-15 minutes. Keep an eye on them; they are done when the cheese is melted and golden brown, and the mussels are bubbling slightly.