Bring a large pot of salted water to a boil for your pasta. While that's heating, pat your chicken breast dry with paper towels. This step matters because wet chicken won't sear properly and you'll end up steaming it instead. Slice the chicken into bite-sized pieces, about 1 to 1.5 inches each.

Heat your olive oil and 1 tablespoon of butter in a large skillet over medium-high heat. Once it's shimmering, add your chicken pieces. Cook for 5-6 minutes per side until golden brown. Don't move them around constantly — let them sit so they actually brown.

You'll hear it sizzle the moment the chicken hits the hot pan, and that's exactly what you want. That sound means the outside is getting that golden crust. After about 6 minutes total, check the thickest piece with a meat thermometer. It should read 165°F inside.

Remove the chicken to a clean plate and set it aside. Drop your fettuccine into that boiling water now. Cook it according to package directions, usually about 9-10 minutes. Don't overcook it — you want it tender but still a little bit firm to the bite.

In the same skillet where you cooked the chicken, melt the remaining 1 tablespoon of butter over medium heat. Add your diced onion and minced garlic. Stir constantly for about 2-3 minutes until the onion starts to soften and turn translucent. Keep the heat at medium — higher and your garlic will burn.

Pour in your heavy cream slowly while stirring. When your kitchen smells like warm, buttery garlic cream, you know you're right on track. Let it simmer gently for 2 minutes. Never let it boil hard or the cream will break and get grainy.

Remove the skillet from heat and stir in your Parmesan cheese, nutmeg, salt, and pepper. Add the cooked chicken back in. Drain your pasta and toss everything together. The residual heat will melt the cheese perfectly and coat every strand of pasta.