Place a large pan over medium heat and add 1 tbsp oil and butter. Once the butter has melted, add the sliced onions and fry until soft and golden. Don't rush this process - it'll likely take around 15 minutes for them to properly soften and lightly caramelise. Once cooked, use tongs to remove them and place in a bowl to one side (wipe out the pan if you need to).
Just before the onions are done, combine the flour and seasoning in a large shallow dish. One by one, coat both sides of the pork chops in the flour, then place to one side.
Add 1 tbsp oil and butter to the now empty pan and turn the heat to medium-high. Once the pan is hot and the butter has melted, add the pork chops to the pan. Fry for around 3 minutes on each side, or until they've built up a golden crust and are just cooked through. Remove and place on a plate to one side.
Lower the heat back down to medium and add the garlic to the leftover fat in the pan. Fry for 10-20 seconds (be careful it doesn't burn), then stir in the cooked onion. Add 2 tbsp flour and stir into the onions, then begin gradually pouring in the stock, stirring as you go to ensure no lumps form. Stir in the cream, Worcestershire sauce and mustard and bring to a gentle simmer.
Stir in the resting juices from the pork, then check for seasoning and adjust with salt and pepper. The gravy should already be thick enough at this point, but if you'd like it a little thicker, just continue simmering for another couple of minutes.
Add the pork back to the pan and cover in the gravy, then serve up and enjoy!