Ingredients

• 4 medium russet potatoes (about 2 pounds), peeled
• 1 1/2 teaspoons kosher salt, divided
• 3/4 teaspoon freshly ground black pepper, divided
• 2 tablespoons vegetable oil
• 3 tablespoons unsalted butter, divided
• 4 medium shallots, thinly sliced
• 6 large eggs, room temperature
• 1 1/4 cups half-and-half
• 1 teaspoon mustard powder
• Pinch of grated nutmeg
• 1 tablespoon finely chopped tarragon
• 5 ounces Fontina cheese, grated (about 1 1/2 cups)
• 4 ounces fresh goat cheese, crumbled (about 3/4 cup)
• 1/2 bunch asparagus (about 1/2 pound), ends trimmed
• A 10-inch cast-iron skillet