Add the butter to a pot over medium-high heat. Once the butter is almost fully melted, add in the flour, crushed red pepper flakes, and garlic. Whisk that continously for about 2 minutes. Then add in the red onions and whisk that continuously for a few minutes until the roux turns a light nutty brown color.

Bring the pot to a boil, add the white wine, and let that cook for a few minutes so the alcohol can burn it. Then add in the lemon juice & dijon mustard, give that a stir, Bring the pot to a simmer, and let that simmer for about 5 minutes.

Boil the rigatoni in salted water until al dente. (Set aside at least 1 cup of pasta water).

In the pot with the sauce, stir in the heavy cream, a ½ cup of pasta water, salt & pepper, and bring the pot to a boil. Once it comes to a boil, lower it to a simmer, and add the sun-dried tomatoes, grated Pecorino Romano, and another ½ cup of pasta water. Give that a stir and let that simmer together for a few minutes.

Then add in the spinach and the cooked rigatoni. Stir that together and let it sit for a few minutes so it can set and thicken up.

Garnish with leftover chopped spinach, cracked black pepper, and grated Pecorino Romano.

Serve & Enjoy!!!!