Simmering the balsamic vinegar both mellows and thickens it. When tossed with the hot pasta and the butter, it forms a smooth, uniquely flavored sauce.
1. Heat the oven to 400°. Snap the tough ends off the asparagus and discard them. Cut the spears into 1-inch pieces. Put the asparagus on a baking sheet and toss with the oil and 1/4 teaspoon each of the salt and pepper. Roast until tender, about 10 minutes.
2. Meanwhile, put the vinegar in a small saucepan. Simmer until 3 tablespoons remain. Stir in the brown sugar and the remaining 1/4 teaspoon pepper. Remove from the heat.
3. Cook the penne in a large pot of boiling, salted water until just done, about 13 minutes. Drain the pasta and toss with the butter, vinegar, asparagus, Parmesan, and the remaining 1 3/4 teaspoons salt. Serve with additional Parmesan.
Variations: Penne with Roasted Broccoli and Balsamic Butter: When asparagus is not in season, cut 1 pound of broccoli into small spears for roasting. Toss them with 2 tablespoons oil and 1/4 teaspoon each of salt and pepper and roast for about 15 minutes. Continue with step 2.
Penne with Roasted Vegetables, Toasted Nuts, and Balsamic Butter: Toss in 1/3 cup of toasted pine nuts, hazelnuts, or walnuts at the end with either asparagus or broccoli.
Wine Recommendation: Balsamic vinegar, Parmesan cheese, and especially asparagus will be best served by a wine with plenty of acidity. Look for a Sancerre from the Loire Valley in France (made from sauvignon blanc grapes) or a sauvignon blanc from Italy.