Asparagus Omelet with Black Forest Ham and Mustard | America's Test Kitchen

Ingredients

• 2 tablespoons unsalted butter
• 1/2 pound asparagus, trimmed of tough ends and cut on bias into 1/4-inch pieces (about 1 1/4 cups)
• 1 medium shallot, halved and sliced thin
• 1 teaspoon fresh lemon juice
• 2 teaspoons whole grain mustard
• 5 large eggs
• 3 ounces Black Forest ham, cut into 1/4-inch dice
• 1 1/2 ounces Gruyère cheese, finely grated (about 1/2 cup)