Cook them in plenty of water for about 2 hours set aside the resulting stock, you can use it for soups and gravies.
Preheat oven to 200 C. Place the marrow bones into an ovenproof dish cut side up, lay it to the oven and roast for 10-15 minutes.
Meanwhile, chop the garlic and shallots.
In a wok or a frying pan, melt the butter an saute the chopped garlic and shallots until fragrant.
Add the washed whole mushrooms, salt and pepper, the wine, half cup of the stock previously produced and half of the lemon juice.
Cover the pan and cook for 10 minutes, then remove the lid and simmer until the sauce reduces. Remove it from the heat and let it cool for a few minutes.
Chop the parsley leaves and add it to the mushroom saute, add the rest of the lemon juice and season with salt and pepper to taste. Stir them lightly.
Heat 1-2 tablespoons olive oil in a large frying pan. Place the bread slices, salt them lightly and fry them golden-brown on both sides.
Serve a pair of hot from the oven roasted marrow bones, some mushroom-parsley salad and toast slices. When eating, scoop out some marrow and spread it on toast, sprinkle some salt and top it with mushrooms-parsley salad.