Lemon Asparagus Pasta

4 ounces whole-wheat penne pasta (about 1 1/2 cups)
1/2 bunch asparagus, trimmed and cut into 3/4-inch pieces
3/4 cup whole milk
2 teaspoons whole-grain mustard
2 teaspoons all-purpose flour
1/8 teaspoon salt
1/4 teaspoon freshly ground pepper
1 teaspoon extra-virgin olive oil
2 tablespoons minced garlic
1 teaspoon minced fresh tarragon or 1/4 teaspoon dried
1/4 teaspoon freshly grated lemon zest
1 teaspoon lemon juice1/2 cup freshly grated Parmesan cheese, divided

Bring a large saucepan of water to a boil. Cook pasta for 6 minutes. Add asparagus and continue cooking, stirring occasionally, until the pasta and asparagus are just tender, about 3 minutes more. Drain and return to the pot.

Meanwhile, whisk milk, mustard, flour, salt and pepper in a medium bowl. Heat oil in a small saucepan over medium-high heat. Add garlic and cook, stirring constantly, until fragrant and lightly browned, 30 seconds to 1 minute. Whisk in the milk mixture. Bring to a simmer, stirring constantly, and cook until thickened, 1 to 2 minutes. Stir in tarragon, lemon zest and juice. Stir the sauce into the cooked pasta and place over medium-high heat. Cook, stirring constantly, until the sauce is thick, creamy and coats the pasta. Stir 1/4 cup Parmesan into the pasta until combined. Serve the pasta topped with the remaining 1/4 cup Parmesan.