In a large skillet, heat olive oil and butter over medium-high heat until shimmering.
Add chicken breasts and sprinkle with salt and pepper.
Cook chicken breasts 4 - 5 minutes per side or until meat thermometer registers 165° F and chicken is done.
Remove breasts to a large plate. Cover and set aside.
Remove all but 1 TBSP drippings from the pan. Add garlic and cook until fragrant, about 1 minute.
Add chicken broth to skillet, scraping brown bits from bottom of pan.
Add thyme and bring mixture to a simmer.
Add cream, Dijon and stone ground mustard. Stir to combine. Bring back to a simmer. Sauce will start to thicken.
Return chicken to the pan and cook additional 3 - 4 minutes until chicken is heated thru and sauce is desired consistency.
Serve chicken with sauce spooned on top.