Cook the pasta + asparagus: Bring a large pot of water to a boil. Cook the pasta according to package directions. In the last 3 minutes of cooking, add the asparagus to the pot. Reserve ½ cup of pasta water, then drain.
Sauté the garlic: While the pasta cooks, heat the olive oil in a large skillet or saucepan over medium heat. Add the garlic and cook for 30 seconds, just until fragrant.
Make a roux: Sprinkle in the flour and whisk constantly for 30–60 seconds.
Make it creamy: Slowly whisk in the plant-based milk. Keep whisking until smooth, then simmer for 2–3 minutes, until the sauce thickens slightly.
Season the sauce: Whisk in the Dijon mustard, nutritional yeast, salt, and pepper.
Add the lemon last: Remove from heat, then stir in the lemon zest and lemon juice.
Toss it all together: Add the drained pasta and asparagus to the skillet with the sauce and toss well. Add a splash of reserved pasta water as needed until the sauce is silky and coats everything beautifully. Serve hot.
