Render the bone marrow and soak your bread rolls:

Add the raw bone marrow into a small saucepan and heat over medium-low heat. Keep the pot on the stove for about 5-10 minutes, until all the fat has been rendered. Strain through a fine mesh-sieve and wait for the fat to re-solidify at room temperature.

In a mixing bowl, pour the hot milk over the bread roll cubes and leave them to soak for at least 15 minutes.

Assemble your dumplings:

Once the bone marrow has solidified, whisk in the eggs and chopped chives until creamy. Add nutmeg, pepper, and salt to taste. Then add the soaked bread roll cubes and breadcrumbs. Mix briefly with your hands. Leave the mixture to sit for 15 minutes before forming dumplings.

Shape and cook your dumplings:

Heat a large pot of lightly salted water until just below a light simmer. Lightly wet your hands and form little ball-shaped dumplings out of your batter. The surface should be completely smooth. Add the dumplings into your poaching liquid and leave them to cook for about 5 minutes or until they float on the surface and are cooked through. Gently drain the dumplings.

Serve the dumplings:

Divide the dumplings among individual soup bowls. Heat the beef broth until lightly simmering and season to taste with nutmeg, vinegar, and salt. Pour the hot broth over the bone marrow dumplings and garnish with chopped chives.