The French use it to flavor steak such as filet mignon. After sauteeing the steak, add some wine reduction sauce and place the bone marrow on top.
Here is a simple recipe (I somewhat translated it from a French site)
For 4 person
4 tenderloin steaks, 1 large beef bones, 150g butter (about 6 tbsp) 4 shallots, 2 1/2 cups of red wine preferably Beaujolais or pinot noir , 4 tablespoons meat glaze, salt and pepper.
Peel the shallots, chop them finely.
Boil water, salt it, add the bones in the boiling water, reduce heat and poach (cook on low simmer) for 5 minutes, remove from heat and leave the bones in the hot water.
Heat butter in a heavy bottomed sauté pan , add the steaks in the hot butter and let cook 2 to 3 minutes per side, depending on desired doneness.
When the meat is cooked, let it rest in a warm oven.
Add the chopped shallots in the same pan where you cooked the steaks
when shallots are soft, add the wine and meat glaze, let it reduce to about half the volume
Cut remaining butter into 4-5 pieces, add to the sauce piece by peace, whisking until integrated into the sauce
Season the sauce with salt and pepper and pour sauce over the steaks
Drain the bones, using a sharp knife, carefully remove the marrow, cut into 4 slices; have 2 slices on each steak, serve immediately on hot plates.
I've used bone marrow all my life. In fact, I think my mother gave it to us as babies, but that could be a family myth. I've always roasted it and used it as part of my regular stock making. And naturally, I have sucked it straight from the bone, in soups, stews, goat curry, etc. This is the first time I've heard of spreading it on bread. Sounds yummy and will definitely give that a try. But I am totally consumed by the idea of eating it with something called onion marmalade! Who has the recipe for that? Want some now, now, now.