01 - Pat chicken breasts dry with paper towels. Season both sides generously with salt and black pepper. Lightly dust each breast with flour, shaking off excess.
02 - Heat olive oil in a large skillet over medium-high heat until shimmering. Add chicken breasts and sear for 4-5 minutes per side until golden brown and cooked through. Remove chicken from skillet and set aside on a plate.
03 - Reduce heat to medium. Add butter to the same skillet. Sauté chopped onions for 2 minutes until translucent. Add sliced mushrooms and cook for 4-5 minutes, stirring occasionally, until browned and tender. Add minced garlic and cook for 1 minute until fragrant.
04 - Pour in chicken broth, using a wooden spoon to scrape up any browned bits from the bottom of the pan. Let the mixture simmer for 2 minutes to reduce slightly.
05 - Stir in heavy cream and thyme leaves. Bring to a gentle simmer, stirring constantly to combine.
06 - Return chicken breasts to the skillet, nestling them into the sauce. Simmer uncovered for 8-10 minutes until chicken is cooked through (165°F internal temperature) and sauce has thickened and coats the back of a spoon.
07 - Taste sauce and adjust seasoning with additional salt and pepper if needed. Transfer to serving plates and garnish with chopped fresh parsley.