Pat the chicken breasts dry with a paper towel and season with salt and pepper.
Heat olive oil in a cast-iron skillet over medium heat and sear chicken breasts.
Remove chicken and saute sliced onion in the remaining oil until caramelized.
Add minced garlic, cook briefly, then stir in flour to blend.
Gradually pour in the chicken broth, whisking continuously until combined.
Add the cream, adjust seasonings, and simmer until thickened.
Return chicken to the skillet and simmer in the gravy until cooked through.
Notes
For best results, let the dish sit for a day to enhance the flavors. Reheat carefully on a stove or microwave, adding a bit of broth to maintain moisture.