Bring a large pot of salted water (about 4-5 liters) to a rolling boil. Add fettuccine and cook until al dente according to package instructions (usually 10–12 minutes). Reserve 1 cup pasta cooking water, then drain pasta and set aside.

Make base for sauce

While pasta cooks, melt 6 tbsp unsalted butter in a wide sauté pan over medium heat. Add minced garlic and cook 30–45 seconds until fragrant (do not brown). Sprinkle 1 tsp flour over the butter/garlic and stir for 30 seconds to remove raw flour taste.

Finish Alfredo

Slowly add 2 cups heavy cream and 1 cup whole milk to the pan, whisking constantly. Increase heat to medium-high and bring mixture to a gentle simmer (do not boil vigorously). Reduce heat to medium-low and simmer 3–4 minutes until slightly thickened. Whisk in 2 cups grated Parmesan cheese, 1.5 tsp salt, 1 tsp black pepper, and 1/4 tsp grated nutmeg (if using). Stir until cheese is melted and sauce is smooth. If sauce becomes too thick, add reserved pasta water 1–2 tbsp at a time until desired consistency is reached (you may need up to 1/2 cup). Keep sauce warm over very low heat.

Toss pasta with sauce

Add drained fettuccine to the sauce pan and toss gently with tongs or two forks until pasta is evenly coated, about 1–2 minutes. Taste and adjust seasoning with salt and pepper as needed. If sauce needs loosening, add more reserved pasta water.

Mushrooms & Scallions

Heat 1 tbsp olive oil and 1 tbsp butter in a separate skillet over medium-high heat until shimmering. Add sliced mushrooms in a single layer (work in batches if pan is crowded). Let mushrooms brown without stirring for 2–3 minutes, then stir and continue cooking 2–3 more minutes until golden and liquid has mostly evaporated. Season with 1/2 tsp salt and 1/4 tsp black pepper. Add thinly sliced scallion whites and cook 30–45 seconds until slightly softened; reserve most of the scallion greens for garnish (stir in the sliced green parts at end). Remove from heat and fold the sautéed mushrooms and most scallions into the sauced fettuccine, keeping a small amount of scallion greens for topping.

Protein (Grilling & Blackening option)

Prepare the protein: pat 1 lb chicken breasts dry and, if thick, butterfly or pound to even thickness (~1/2"–3/4"). Brush both sides with 1 tbsp olive oil and season with 3/4 tsp salt and 1/2 tsp black pepper. If choosing blackened, sprinkle 1 tsp blackening spice evenly on both sides and press gently to adhere.

Preheat a grill or grill pan to medium-high heat (about 400°F / 200°C). Grill chicken 4–6 minutes per side (depending on thickness) until internal temperature reaches 165°F (74°C) and juices run clear. Remove and let rest 5 minutes, then slice thinly on the bias.

Alternative proteins: If using shrimp, scallops, or steak, season similarly and grill to preferred doneness (shrimp 2–3 minutes per side; steak 3–5 minutes per side depending on thickness). Adjust resting time before slicing.

Tossing with pasta: Arrange sliced grilled protein on top of or gently folded into the sauced fettuccine and mushrooms. Spoon any resting juices from the protein over the pasta for extra flavor.

To Serve

Plate 3–4 oz (about 1/6 of prepared batch) of sauced fettuccine per serving, top with sliced grilled protein, a sprinkle of reserved scallion greens, chopped parsley (optional), and extra grated Parmesan. Serve immediately with warm sliced French bread on the side.

If offering blackened option, note an up-charge: blackened spice is optional and will add additional smoky heat. Taste before serving and provide lemon wedges if desired to brighten the dish.