These are expected at every holiday meal and family gathering. My Aunt Fran makes them best, and she handed down the recipe to me. Although cheesy onions usually arrive at the table in a casserole dish, cuddled in a decorative kitchen towel, like the precious gems they are, you can make them on the fly and serve them up in a saucepan as the side dish to any savory protein (which is how they most often appear in my apartment).
10 ounces pearl onions, peeled
2 tablespoons unsalted butter
2 tablespoons all-purpose flour
1 teaspoon yellow mustard
1⁄2 cup whole milk
6 ounces Velveeta cheese, chopped 2 teaspoons kosher salt
1⁄8 teaspoon black pepper
Put the pearl onions in a saucepan, add enough water to just cover them, bring to a boil, and cook until the onions are knife-tender, 3 to 5 minutes. Drain the onions and transfer to a heatproof bowl or small serving dish.
Make the cheese sauce. Melt the butter in a small saucepan over medium-low heat. Add the flour and whisk until smooth and the mixture comes to a boil. Add the mustard and do the same. Repeat with the milk. Stir in the Velveeta until melted. Season with the salt and pepper.
Pour the sauce over the onions and serve.