Bring a large pot of salted water to a boil. Cook the shells until al dente. Set aside. Return the pot to the stove.
While the pasta is cooking, prep all the ingredients needed for the recipe.
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.
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 ½ 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.
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.
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.
Divide the cooked shells between bowls and garnish with more parsley if desired. Enjoy!
