1 leek, diced
1 carrot, peeled and diced
1 onion, diced
1 celery rib, diced
1 tomato, seeded and diced
2 cloves garlic
2 sprigs thyme
1 teaspoon white peppercorns
4 1/2 cups water
1 bunch asparagus (about 1/2 pound)
1/2 cup ricotta cheese
1/4 pound fontina cheese, grated
Salt and freshly ground black pepper
1 pound pasta dough (you can use prepared dough)
1 egg, lightly beaten
1 tablespoon white truffle oil
Combine leek, carrot, onion, celery, tomato and garlic. Place in a saucepan with thyme, peppercorns and water. Bring to a boil and simmer for an hour. Strain and return to the heat. Reduce until only a little over a cup is left to create an essence.
Prepare asparagus by lightly peeling and removing the tough part of the stem. Cut into 3/4-inch sections and cook in lightly salted boiling water until tender, about 3 minutes. Remove and cool in ice water. Put asparagus tips aside as a garnish.
For the filling, place the remaining asparagus in a food processor and pulse a few times to create a not-too-fine mince. Mix in a bowl with the ricotta and fontina; season with salt and freshly ground black pepper.
For freshly made pasta, place pasta machine on the counter. Lightly dust the counter with flour before starting, to avoid the dough sticking. Work the dough through the rollers starting on the thickest setting and gradually reducing the settings until you achieve thin sheets, about as thick as heavy paper. Lay out the sheets, and use a ring cutter to cut circles of approximately 2 1/2 inches in diameter. Spoon a dab of asparagus mixture in the center of each circle. Brush the outside of the circles with a little beaten egg and fold to create half-moon shapes. Pull the tails around to make the tortellini and seal with a bit of beaten egg.
Cook the tortellini in salted, gently simmering water until they float to the top. Heat up the vegetable essence and ladle into wide bowls to a depth of about a quarter-inch. With a slotted spoon, place tortellini in the essence and drizzle with white truffle oil. Serves 4.