Preheat the oven to 450°F (230°C). Place the bone marrow on a baking sheet and roast for about 15-20 minutes, or until the marrow is soft and starting to bubble. Remove from the oven and let cool slightly.

In a bowl, combine the softened butter, minced garlic, chopped parsley, lemon zest, and a pinch of salt and pepper. Once the bone marrow has cooled enough to handle, scoop the marrow from the bones into the butter mixture. Mix well until thoroughly combined. Shape the butter into a log using plastic wrap and refrigerate until firm.

Season the ribeye steaks generously with salt and pepper on both sides. Heat the olive oil in a large skillet over medium-high heat.

In the hot skillet, add the sliced leeks and sauté until they are crispy and golden brown, about 5-7 minutes. Remove and drain on paper towels.

In a shallow dish, combine the crispy leeks, chopped marjoram, and panko breadcrumbs. Press the mixture onto both sides of the seasoned ribeye steaks, ensuring an even coating.

In the same skillet, add the ribeye steaks and cook for about 4-5 minutes on each side for medium-rare, or to your desired doneness. Use a meat thermometer to check for an internal temperature of 130°F (54°C) for medium-rare.

Once cooked, transfer the steaks to a cutting board and let them rest for 5 minutes. Slice the steaks and serve topped with slices of the roasted bone marrow compound butter.