1. Prepare the Chicken: Pat the chicken breasts or thighs dry with paper towels. If using breasts, slice them horizontally to create thinner cutlets, about 1/2-inch thick. This helps them cook faster and more evenly. Season both sides of the chicken with salt, pepper, and Italian seasoning.

2. Sear the Chicken: Heat the olive oil in a large skillet or frying pan over medium-high heat. Once the oil shimmers, add the seasoned chicken. Cook for 4-6 minutes per side, until golden brown and cooked through. The internal temperature should reach 165 F (74 C). Remove the chicken from the skillet and set aside on a plate, tented loosely with foil to keep warm.

3. Saute the Garlic: Reduce the heat to medium. Add the minced garlic to the same skillet and cook for about 1 minute, stirring constantly, until fragrant. Be careful not to burn the garlic, as it can turn bitter quickly.

4. Deglaze and Build the Sauce Base: Pour in the chicken broth, scraping up any browned bits from the bottom of the pan with a wooden spoon. These bits are full of flavor! Bring the broth to a simmer.

5. Thicken the Sauce: In a small bowl, whisk together the cornstarch and cold water until smooth to create a slurry. Slowly pour the cornstarch slurry into the simmering broth in the skillet, whisking continuously. Continue to whisk until the sauce thickens to your desired consistency, usually within 1-2 minutes. It should be thick enough to coat the back of a spoon.

6. Add Creaminess and Finish: Stir in the milk and grated Parmesan cheese. Cook for another 1-2 minutes, stirring until the cheese has melted and the sauce is smooth and creamy. Taste the sauce and adjust seasonings if needed.

7. Combine and Serve: Return the cooked chicken to the skillet, spooning the creamy garlic sauce over it. Let it warm through for a minute or two. Garnish with fresh chopped parsley, if desired, and serve immediately.