2 lb. asparagus, trimmed
4 c. fresh spinach, cooked and drained
1 c. sun-dried tomato
7 large eggs
1 1/3 c. whole milk
2 tbsp. freshly grated Parmigiano-Reggiano
1 1/4 tsp. salt
1/2 tsp. black pepper
1/8 tsp. freshly grated nutmeg, or to taste
Put oven rack in middle position and preheat oven to 325°F.
Butter an 8-by-2-inch round cake pan or individual soufflé cups and line the bottom with a round of wax paper, then butter paper. Steam asparagus, covered, for six to eight minutes, or until tender. Purée asparagus, sun-dried tomato, and spinach in a food processor until smooth, one to two minutes. You will have about three cups of purée.
Whisk together eggs, milk, cheese, salt, pepper, and nutmeg in a bowl, then whisk in asparagus mixture. Pour mixture into the pan and bake in a hot water bath until flan is set, about 50 minutes to one hour, and a toothpick inserted in center comes out clean. Transfer pan to a rack to cool slightly, about 10 to 15 minutes.
Run a thin knife around the edge of the flan to loosen, then place a serving plate over pan and invert flan onto plate. Remove pan and discard paper. Cut flan into wedges and serve immediately.