Begin by bringing a large pot of salted water to a rolling boil over high heat. Once boiling, add your choice of pasta and cook until al dente, usually around 8-10 minutes. Reserve about 1 cup of pasta water, then drain the rest in a colander.

In a large skillet, melt 3 tablespoons of butter over medium heat. Season chicken with salt and black pepper, then add them to the skillet. Sauté the chicken for about 6-8 minutes per side until golden brown and cooked through. Remove from the skillet and let it rest.

In the same skillet, reduce heat and add an additional tablespoon of butter. Once melted, add minced garlic and cook for about 1 minute until fragrant.

Stir in Dijon mustard, lemon juice and zest, red pepper flakes, and dried thyme or Italian seasoning. Cook for an additional minute.

If using heavy cream, slowly pour in about ½ cup and stir to combine. Let the sauce simmer for 2-3 minutes, allowing it to thicken.

Slice the cooked chicken into bite-sized pieces and return it to the skillet. Add the drained pasta and a splash of reserved pasta water, tossing everything to coat in the sauce.

Finally, stir in grated Parmesan cheese and chopped parsley. Mix until the cheese melts into the sauce, then adjust seasoning with salt and pepper.