Bring a large pot of salted water to a boil. Cook the shells until al dente. Set aside. Return the pot to the stove.
Prep the Ingredients:
While the pasta is cooking, prep all the ingredients needed for the recipe.
Cook the Aromatics:
Heat the neutral cooking oil in the pot over medium heat. Add the onion and cook for 5 minutes. Add the garlic and red Fresno chili pepper and cook for 1 minute until fragrant.
Prepare the Roux:
Melt the butter into the aromatics and sprinkle the flour on top and stir to coat. Cook for 2-3 minutes or until the flour becomes aromatic and golden.
Slowly add the stock in 1/2 cup increments, whisking after each addition, until all the stock has been added. Bring to a very low boil and then reduce heat. Whisk in the warm heavy cream and season to taste with salt and pepper.
Cook the Asparagus:
Add the asparagus to the pot and cook for 3-4 minutes or until it is bright green and tender-crisp. Add the lemon juice and parsley and toss to combine. Taste and season again to your preferences.
Finish the Pasta:
Add the pasta to the pot and toss to combine until all the pasta is coated with the sauce. Cook over low heat for 1-2 minutes more to thicken the sauce further and to warm up the pasta. Turn off the heat.
To Serve:
Divide the cooked shells between bowls and garnish with more parsley if desired. Enjoy!