Preheat oven to 325 degrees.

Arrange asparagus on a baking sheet and cook for 7-9 minutes, until asparagus is just hinting at fork tender. Do not overcook. (You can also steam asparagus in microwave.)

Bring a large pot of water to a boil. Cook pasta according to instructions until just al dente. When pasta has finished cooking drain, reserving 1/2 c of the pasta water for the sauce.

While the pasta is cooking, heat the olive oil over medium heat.

Add the garlic and saute for 30 seconds to 1 minute. If garlic begins to brown, turn down heat.

Add the asparagus and salt and cook for an additional minute, tossing to thoroughly combine, then remove from heat.

In a small bowl, whisk the egg yolk then mix with the Parmesan and 1/3 c of the pasta water.

Return the pasta to the pot and add the egg yolk mixture. Cook over medium heat for about 2 minutes, until sauce is thick and pasta coated. If the sauce gets too thick, add additional pasta water. Toss in the asparagus and season with additional salt to taste.

Top with lemon zest before serving.