Pasta with Asparagus

1 lb asparagus, cut into 1 inch pieces, using only the tips and tender parts of the stem
1 lb dried pasta
5 tbsp unsalted butter
1/2 tbsp finely chopped onion
1/2 cup heavy cream
nutmeg, salt, and black pepper
2 tbsp freshly grated Parmesan, plus additional to serve

1. Cook asparagus in a pan of boiling, salted water until just tender – about 3 – 5 minutes. Drain and plunge into cold water until completely cooled. Drain and reserve.
2. Cook the pasta in a large pot of boiling, salted water, until al dente.
3. While the pasta is cooking, melt butter in a skillet. Add onion and cook, stirring occasionally over medium heat, until soft, 5 minutes.
4. Add asparagus and cream and simmer gently until the cream is just thickened, 1 – 2 minutes.
5. Add nutmeg, salt, and pepper to taste.
6. Drain pasta, reserving 1/2 cup pasta water. Add pasta with Parmesan to the hot sauce and toss gently, adding reserved water as needed.
7. Serve immediately with additional Parmesan.