Bone Marrow Toast Recipe

Heat 1 tablespoon olive oil in a medium skillet over medium heat. Add the thinly sliced red onions and cook, stirring occasionally, until softened, about 6–8 minutes.

Sprinkle in the granulated sugar and continue to cook, stirring, until the onions begin to caramelize, about 6–8 more minutes. Reduce heat if browning too quickly.

Stir in the red wine vinegar and balsamic vinegar, scraping up any browned bits. Simmer until the liquid reduces and the onions are jammy, about 4–6 minutes. Season with 1/2 teaspoon kosher salt and 1/4 teaspoon black pepper. Remove from heat and let cool slightly.

In a small bowl combine 3 tablespoons sour cream, 2 teaspoons prepared horseradish, 1 tablespoon mayonnaise, 1 teaspoon lemon juice, 1 teaspoon kosher salt, and 1/2 teaspoon black pepper. Whisk until smooth and taste-adjust salt and horseradish. Chill in fridge while other components are prepared.

Preheat oven to 450°F (230°C). Arrange the split marrow bones cut-side up on a rimmed baking sheet or cast-iron pan. Scatter smashed garlic cloves and thyme sprigs around the bones.

Season the marrow lightly with 1 tablespoon kosher salt and 1 teaspoon black pepper, rubbing into exposed marrow. Roast in the preheated oven until marrow is bubbling and edges are browned, about 15–20 minutes depending on bone size. Do not overcook to the point marrow fully melts away.

Remove from oven and let rest 2–3 minutes. Discard garlic and thyme sprigs. Using a small spoon, loosen marrow from the bone if needed and transfer or serve directly on toast as directed below.

While marrow roasts, brush both sides of the bread slices with softened butter. Toast in a skillet over medium heat or under the broiler until golden and crisp on both sides (about 2–3 minutes per side in a skillet or 1–2 minutes per side under broiler).

Place the hot toasted bread on a baking sheet. Top each slice lightly with shredded or sliced fontina (use approximately 2 tablespoons per slice). Put the bread briefly under the broiler (or in a hot oven at 450°F) just until the fontina melts and begins to bubble, about 1–2 minutes—watch closely to avoid burning.

Spoon warm roasted bone marrow onto the fontina-melted toasts. The marrow should be soft and spreadable; use a small spoon to distribute evenly (about 1 marrow bone per 2 slices, adjust as needed).

Dot each toast with about 1 teaspoon of red onion jam and a generous teaspoon of horseradish crème. Finish with a sprinkle of chopped parsley (optional) and a light squeeze of lemon wedge to brighten.

Serve immediately while marrow and cheese are warm. Provide extra lemon wedges at the table.