Cook pasta in boiling water for 6 minutes. Add asparagus and continue cooking until just tender (about 3-5 more minutes). Drain and return to the pot.
In a medium bowl, whisk milk, mustard, flour, salt and pepper.
Heat oil in a small saucepan on medium-high heat. Add garlic and cook until fragrant and lightly browned (stirring constantly) about 1 minute. Pour in the milk mixture and whisk. Continue stirring as you bring to a simmer. Cook until thick, 1 to 2 minutes. Stir in lemon zest and juice.
Stir this sauce into the pasta and cook over medium-high heat. Cook until sauce is thick and creamy. Mix grated Parmesan cheese into the pasta.
Top with remaining shredded Parmesan cheese as a topping. ENJOY!