Bring a large pot of salted water to a boil. Add the fettuccine and cook according to package directions until al dente, about 8–10 minutes. Drain and set aside.
While the pasta cooks, heat 2 tablespoons unsalted butter in a large saucepan over medium-high heat. Season the chicken pieces with 1/2 teaspoon salt and 1/2 teaspoon pepper.
Add the seasoned chicken to the hot pan and cook, stirring occasionally, until golden and cooked through, about 8 minutes. Remove the chicken from the pan and set aside.
In the same pan, melt the remaining 8 tablespoons of butter over medium heat. Stir in the ricotta, heavy cream, and 2/3 cup grated Parmesan until smooth.
Bring the sauce to a gentle boil, then reduce heat to medium-low and simmer for about 5 minutes, stirring occasionally, until slightly thickened. Taste and adjust seasoning with salt and pepper as needed.
Return the cooked chicken to the saucepan, add the drained fettuccine, and toss to coat in the sauce. Cook together briefly until heated through.
Serve immediately, garnished with additional Parmesan and chopped parsley.
