1) Heat the oven
Heat oven to 450°F. Line a rimmed baking sheet with foil if you want easy cleanup. Set marrow bones cut-side up on the pan (a light slick of neutral oil helps prevent sticking, but is optional). Pat bones dry and season the exposed marrow generously with kosher salt and black pepper.
If you soaked the bones: Drain, rinse, and pat very dry before seasoning so they roast instead of steam.
2) Roast the marrow
Roast for 12 to 18 minutes, depending on bone size. You are looking for marrow that is soft and jiggles slightly when you nudge the pan. It should look glossy and spoonable, not totally liquefied, and it should be piping hot.
Quick tip: If your bones are different sizes, pull the smaller ones first and let the bigger ones finish.
Also: Marrow can drip. A rimmed pan helps a lot. If you are worried about smoke, keep your oven clean and consider placing a second tray on the rack below to catch any stray drips.
3) Make the parsley salad
While the bones roast, mix parsley, shallot, capers (if using), lemon zest, lemon juice, olive oil, salt, and crushed red pepper. Taste. It should be punchy and bright, like it is trying to wake up the marrow.
4) Make the garlic toast
Brush bread with olive oil or butter. Toast in a skillet over medium heat until crisp and golden, 2 to 4 minutes per side.
Or toast in the oven for about 6 to 8 minutes total, flipping halfway, until evenly golden.
While still warm, rub one side of each toast with the cut garlic clove. Finish with a pinch of flaky salt.
5) Serve
Bring the hot bones to the table. Spoon marrow onto toast, top with a little parsley salad, and eat immediately while everything is hot and crisp.
Optional extra credit: Add a tiny squeeze of lemon on top right before you bite. And do not be shy with flaky salt at the table. Marrow loves it.
