2 lb. pearl onions, fresh or frozen
5 Tbs. (1/2 stick) unsalted butter
1 yellow onion, minced
2 1/2 Tbs. all-purpose flour
2 cups of whole milk
1/4 tsp. freshly grated nutmeg
Salt and freshly ground pepper, to taste
1 cup shredded Gruyere Cheese
3/4 cup fine dried white bread crumbs
If you are using fresh onions, here's what you have to do:
Bring a saucepan half full of salted water to a boil over high heat. Add the pearl onions and cook for 2 minutes. Using a slotted spoon, scoop out the onions, rinse with cold water and drain. Reserve the water in the pot. Trim off the ends of each onion, then cut a shallow X into each trimmed end. Squeeze each onion gently to slip off the skin.
Bring the water back to a boil. Add the onions, reduce the heat to low and simmer, uncovered, until the onions are soft when pierced with a knife, 15 to 20 minutes. Using the slotted spoon, transfer the onions to a bowl.
If you are using frozen onions, which I highly recommend, just follow package directions, cook and drain.
Position a rack in the upper third of an oven and preheat to 375°F.
In a saucepan over medium heat, melt 4 Tbs. of the butter. Add the minced onion and cook, stirring occasionally, until soft, about 7 minutes. Add the flour and cook, stirring constantly with a wooden spoon, until well mixed and bubbling, about 2 minutes. Add the milk and cook until the sauce boils and thickens slightly, 3 to 4 minutes. Add 1/2 cup of the cheese. Add the nutmeg and season with salt and pepper. Add the pearl onions, adjust the heat to a gentle simmer and cook until the onions are hot, about 3 minutes.
Transfer the onion mixture to a 2-quart baking dish and sprinkle the bread crumbs and the rest of the cheese evenly over the top. Add a dash of paprika. Cut the remaining 1 Tbs. butter into 6 equal pieces and dot the bread crumbs evenly with the butter. Bake until the crumbs are golden and small bubbles appear along the edges of the dish, 15 to 20 minutes. Serve immediately.