Preheat the oven to 400 degrees Fahrenheit. Place the chicken breasts (either fresh or frozen) in an 8×8 inch pyrex or ceramic baking dish. Season with freshly cracked salt & pepper, and cover the baking dish with foil.

Bake the chicken in the oven until an instant read thermometer inserted into the thickest part of the breast registers 165 degrees Fahrenheit. This could take anywhere from 20 to 50 minutes, depending on the size of your chicken breasts and whether your breasts were frozen or not when you put them in (it will take longer if you put them in frozen). Check them at 20 minutes, and go from there.

When the chicken breasts are done, remove from the oven, transfer to a cutting board, and let rest until the rest of the meal is done.

While the chicken is cooking, bring a large pot of salted water to a rolling boil. Add the fettuccine and cook according to package directions until al dente (usually about 10 minutes). When the pasta is done, drain and set aside.

As the pasta cooks, melt the butter in a large nonstick skillet over low heat, stirring constantly to prevent browning. Add the sliced garlic and ½ tablespoon of rosemary (reserving the other half for garnish) and stir until fragrant. Add the half and half & bring to a simmer. Whisk constantly with a rubber whisk for about 5 minutes, until slightly thickened. Turn off the heat and stir in the parmesan cheese. Season liberally with salt and pepper.

Add the pasta and peas to a large serving bowl and toss with the alfredo sauce. Slice the chicken breasts crosswise into slices. Plate the pasta and top each serving with chicken. Sprinkle with the extra minced rosemary, season with freshly cracked salt and pepper and extra cheese, if desired.