Preheat your oven to 400°F (200°C). Place the bone marrow in a roasting pan and roast for about 15-20 minutes until it is soft and bubbly. Remove from the oven and let it cool slightly.

In a mixing bowl, combine the roasted bone marrow, softened butter, chopped parsley, lemon juice, and minced garlic. Mix until well combined and creamy. Season with salt and pepper to taste. Set aside.

In a dry skillet over medium heat, add the fennel seeds and toast for about 2-3 minutes until fragrant, stirring frequently to avoid burning. Remove from heat and let cool.

Once cooled, combine the toasted fennel seeds with the cracked mustard seeds in a small bowl.

Pat the New York strip steaks dry with paper towels. Rub both sides of the steaks with olive oil, then season generously with salt and pepper.

Press the fennel and mustard seed mixture onto both sides of the steaks, ensuring an even coating.

Heat a cast-iron skillet over high heat until very hot. Add the steaks to the skillet and sear for about 3-4 minutes on each side for medium-rare, or longer to reach your desired doneness. Use a meat thermometer to check the internal temperature (130°F for medium-rare).

Once cooked, transfer the steaks to a plate and let them rest for about 5 minutes.

Slice the steaks against the grain and serve topped with generous dollops of whipped bone marrow butter. Garnish with additional parsley if desired.