Black garlic has a really lovely deep umami flavor that reminds me of licorice and balsamic vinegar. It is quite sweet and salty at the same time, with a hint of garlic in the background.
Essentially, it’s just fresh heads of garlic that are left at a particularly low temperature, 60-90C with a specific humidity for, I think, a couple of weeks. The heads are dried and cooked, turning from the wonderful cream color we know to totally black and wrinkled.
At Ottolenghi we use Sweet & Savory black garlic. I use it a lot with grease. I make a black garlic butter: I crush the black garlic with the edge of a knife or pestle, then beat or mix it with softened butter. If I roast a chicken, even a turkey, I often put this black garlic butter under the skin. It gives the chicken a nice flavor and the cooking liquids, the base of a sauce, have a particular depth of black garlic.
I also use it for vegetarian and vegan cooking. I would use it in a vegan lentil and barley bolognese, and it works great for a risotto. I also like to mix it with other garlic. In the latest book, Sabor, we have a recipe for three garlic butters. By three garlic I mean black garlic, confit garlic and raw garlic. Together it gives you all these iterations of garlic. To make a quick yogurt sauce, crush black garlic cloves and add them to yogurt with fresh garlic. It makes the most beautiful barbecue-style sauce that is great on grilled vegetables.