If you're saving your "cheat" day for a bowl of this decadent chicken dinner, you'll have no regrets. Heavy cream, Parmesan cheese, and mushrooms unite with chicken thighs in this worthy pasta that's family friendly and easy too.
Cook pasta in a large pot of generously salted water until al dente. Reserve 1 1/2 cups pasta water; drain.
Season chicken with salt and pepper. Melt 1 tablespoon butter in a large skillet over medium-high heat. Brown chicken, flipping once, until cooked through, 6 to 8 minutes; transfer to a plate. Reduce heat to medium; melt remaining 1 tablespoon butter. Cook shallots and mushrooms, stirring, until golden brown, about 8 minutes. (If skillet browns too quickly, add a little pasta water.) Add wine, bring to a boil, and reduce by half. Slice chicken; add to pan with cream, Parmesan, 1 cup pasta water, and pasta. Toss until sauce coats pasta, adding more pasta water if needed. Add celery and parsley; toss to combine. Serve with Parmesan.