Ingredients

• 2 lb asparagus, trimmed
• 4 large eggs
• 1 1/3 cups whole milk
• 2 tablespoons freshly grated Parmigiano-Reggiano
• 1 1/4 teaspoons salt
• 1/2 teaspoon black pepper
• 1/8 teaspoon freshly grated nutmeg, or to taste
• 1/4 lb Italian Fontina, rind discarded and cheese coarsely grated (or cut into 1/4-inch dice if too soft to grate)
• 1/2 cup whole milk
• 2 large eggs yolks
• 1 tablespoon butter

Instructions

1. Put oven rack in middle position and preheat oven to 325°F. Butter an 8- by 2-inch round cake pan and line bottom with a round of wax paper, then butter paper. 3Steam asparagus in a steamer set over boiling water, covered, until very tender, 6 to 8 minutes. Purée asparagus in a food processor until smooth, 1 to 2 minutes. (You will have about 2 cups purée.)
2. Whisk together eggs, milk, cheese, salt, pepper, and nutmeg in a bowl, then whisk in asparagus purée.
3. Pour asparagus mixture into pan and bake in a hot water bath until flan is set and a wooden pick or skewer inserted in center comes out clean, 50 minutes to 1 hour.
4. Transfer pan to a rack to cool slightly, 10 to 15 minutes.
5. Make sauce while flan cools: Put all sauce ingredients in a metal bowl, then set bowl over a pan of barely simmering water. Heat sauce, whisking until cheese and butter are melted, and then stirring with a wooden spoon, until sauce is slightly thickened and registers 165°F on an instant-read thermometer, 5 to 8 minutes. Remove bowl from pan.
6. Put all sauce ingredients in a metal bowl, then set bowl over a pan of barely simmering water. Heat sauce, whisking until cheese and butter are melted, and then stirring with a wooden spoon, until sauce is slightly thickened and registers 165°F on an instant-read thermometer, 5 to 8 minutes. Remove bowl from pan.
7. Run a thin knife around edge of flan to loosen, then invert a serving plate over pan and invert flan onto plate. Remove pan and discard paper. Cut flan into wedges and serve immediately with sauce.