Preheat the oven to 350 degrees F.
Place the onion halves and thyme sprigs in a 2-inch deep baking tray. Pour the mushroom stock and half the butter over the onions. Bake in the oven for 30 minutes. Remove from the oven and let cool for 15 minutes.
Scoop out the center of the onions. Heat the rest of the butter and the olive oil
in a saute pan over medium-high heat. Add the garlic and saute for 2 minutes. Then add the lobster mushrooms and cook for 5 minutes. Add the chopped parsley and season with salt and pepper. Fill the center of the baked onion rings with the lobster mushroom mixture.
To plate, divide the Creamed Spinach onto center of the 6 plates. Place the lobster
mushroom filled onions onto the spinach
. Finish by spooning the Bourguignon Trimming Sauce over top.