In a small bowl mix 1 tablespoon of the Cajun seasoning and 1 teaspoon black pepper. Rub 3 pounds boneless skinless chicken, pieces with the spice mixture on both sides.
Heat 1 tablespoon olive oil and 1 tablespoon unsalted butter in a large skillet over medium-high heat. Add the seasoned chicken to the pan and cook it for about 3 minutes on each side, until just seared but not fully cooked. Remove the chicken from the pan and set aside.
Add ½ cup chopped onion and 3 teaspoons minced garlic, to the pan and cook until the onion is tender, about 2-3 minutes. Whisk 2 tablespoons all-purpose flour into the pan to create a paste.
Slowly pour in 1 cup chicken broth, 1 cup heavy whipping cream, ½ cup grated parmesan cheese, and the remaining tablespoon of Cajun seasoning. Reduce the heat to medium-low.
Return the chicken to the skillet and cook for another 5-8 minutes until the chicken is cooked through. Season to taste with salt if needed. Garnish with fresh parmesan cheese and red pepper flakes, if desired, and serve!