Broccoli Croque Madame

Name: Broccoli Croque Madame
Ingredients: 2 tablespoons unsalted butter; 2 tablespoons all-purpose flour; 1 1/2 cups whole milk; 1 1/4 cups coarsely grated Gruyère cheese (about 5 ounces); 1 teaspoon Dijon mustard; Kosher salt and freshly ground pepper; 4 cups broccoli florets, halved or quartered into bite-size pieces (about 8 ounces); 2 tablespoons canola or vegetable oil; 8 ounces thinly sliced ham (about 8 slices); 4 large slices crusty white bread (about 1/2 inch thick); 4 large eggs; Cornichons, for serving