Heat the olive oil and butter in a large pan with a lid. Add the onion and cook for 5 minutes until soft.
Add the sliced mushrooms and cook for 5 minutes until golden and all the moisture has cooked off.
Add the garlic and thyme, stir for 1 minute until fragrant.
Tip in the rice and stir to coat each grain in the buttery mixture. Pour in the vegetable stock and stir well.
Bring to the boil, then reduce the heat to low. Cover with a tight-fitting lid and cook for 12-15 minutes without lifting the lid.
Remove from the heat and let it sit for 3 minutes. Fluff with a fork, stir through the cream and most of the parsley. Season generously and serve with the remaining parsley on top.