Spaetzle with Gruyère and Caramelized Onions

Ingredients

• 1 3/4 cups milk
• 1/4 teaspoon freshly grated nutmeg
• 1 medium white onion, thinly sliced
• 3 cups all-purpose flour
• 1 large egg
• 2 tablespoons peanut oil
• 4 large egg yolks
• 1 tablespoon unsalted butter, cut into small pieces
• 1 1/2 cups shredded Gruyère cheese (5 ounces)
• Salt and freshly ground pepper