5 ounces cream
1½ ounces crème fraîche
2 ounces rendered marrow fat
18 peeled cipollini onions
1 sweet onion, quartered
1 tablespoon Arborio rice
6 strips cooked bacon
5 ounces reduced, hot beef jus
For the Bone Marrow Sformatino:
Preheat the oven to 325ºF. Warm the cream and crème fraîche in a small pot over medium heat. Crack the eggs into a separate container and transfer to a Vita-Prep. Blending the eggs slowly, pour the warmed cream and crème fraîche mixture into the Vita-Prep with the machine running until combined. Blend in the melted marrow fat next, and season with the salt before switching off the Vita-Prep. Coat 2-ounce ceramic or foil baking cups with the non-stick spray, then fill with the cream and egg mixture. Bake the cups set in a covered water bath in the oven until just set, about 20 minutes.
For the Caramelized Cipollini Onions:
Pan-roast the cipollini onions in a little oil until tender and caramelized, then set aside.
For the Onion Purée:
In a covered pan, steam the sweet onion and rice with a few tablespoons of water over low heat. When the mixture is completely soft and the rice is well-cooked, remove from the heat. Purée the rice mixture in a Vita-Prep with the butter, olive oil, and salt.
To Assemble and Serve:
Warm the serving plates and spoon a dollop of the onion purée onto each plate. Remove the marrow sformatini from the molds and place one on each plate. Distribute the caramelized onions evenly among the six plates. Do the same with the cooked bacon pieces. Drizzle each plate with the beef jus. Dress the watercress leaves with olive oil and salt and scatter over the top of the jus. Grate the fresh horseradish over each plate with a microplane and finish with a sprinkling of sea salt.