Horizontally slice each chicken breast right through the centre to create 4 even-sized cutlets.
In a large shallow dish, combine the flour, salt and pepper. One by one, take a chicken cutlet and coat it in the flour. Give it a shake and place to one side, then repeat with the remaining cutlets.
Place a large pan over medium-high heat with the butter and oil. Once the butter has melted and the pan is hot, add the cutlets and fry for 3-4 minutes each side until golden (they should be cooked through at this point). Remove the cutlets and place on a plate to one side, leaving any excess fat in the pan.
Lower the heat to medium and fry the garlic for 30 seconds or so (be careful it doesn't burn). Pour in the stock, then swiftly stir in the honey, Dijon and wholegrain mustard until it blends (it might split at the start, but keep whisking and it'll come together). Add the thyme and bring to a simmer for 3-5 minutes until the sauce thickens.
Stir in the resting juices from the chicken, then swiftly stir in the butter until it blends into the sauce. At this point the sauce should be a thin syrupy consistency. Check for seasoning and adjust if needed.
Add the chicken and baste in the sauce, then serve up and enjoy!