Prepare the chicken: If you purchased regular chicken breasts, slice them in half horizontally to make two thinly sliced fillets. Pat each piece of chicken dry with paper towels. Remove the heavy cream from the refrigerator.
Season the chicken: In a medium bowl, toss the chicken breasts with 1 tablespoon of olive oil and the blackened seasoning until evenly coated. Cover and let the chicken sit at room temperature for 15-30 minutes (time allowing).
Bring a large pot of salted water to a boil. Once boiling, reduce the heat to a simmer and cover with a tight fitting lid.
Cook the pasta (see notes): Return the water to a boil. Add the fettuccini pasta (or preferred type of pasta) and cook for 8-12 minutes, or until al dente. Be careful not to overcook the pasta. Reserve 2-3 cups of pasta water, then drain and set aside.
Cook the chicken: Heat the remaining tablespoon of olive oil in a large skillet set over high heat. Once the pan is HOT, add the chicken and cook for 4-6 minutes per side, or until deeply browned and fully cooked. Use a digital meat thermometer to check the internal temperature of the chicken. It should be removed from the pan and set aside when it registers 160-165℉. Sauté the aromatics: Return the same skillet to medium heat. Melt the butter and add the shallots. Cook for 4-5 minutes, or until softened and lightly browned. Reduce the heat to medium-low to prevent burning. Stir in the garlic and cook for 30 seconds, or until fragrant.
Note: By this point, the pasta should be fully cooked. If it's not, that's okay. Use a measuring cup to scoop 1 cup of starchy pasta water from the pot.
Deglaze the skillet: Add about 1 cup of the reserved pasta water to the skillet. Use a large metal spoon or spatula to scrape up any browned bits stuck to the bottom of the pan. Bring to a simmer, then reduce the heat to low.
Make the Alfredo sauce: Stir in the room temperature heavy cream, immediately followed by the cooked pasta. Toss continuously to emulsify the sauce and help it thicken. Add additional pasta water as needed (I typically add at least 1 more cup).
Stir in the Parmesan cheese: Remove the skillet from heat and stir in the blended (or grated) Parmesan cheese until fully melted, creamy, and smooth.
Return the chicken and serve: Slice the blackened chicken breasts into thin strips and serve them over the creamy Alfredo pasta. Season with salt and black pepper, to taste, and garnish with fresh basil if desired. Enjoy!