Place the mushrooms and a couple of cups of beef stock in a small pot. Simmer to reconstitute the mushrooms.
Boil 1 3/4 cups water in a saucepot, season with a little salt, add the kasha and stir. Cover and reduce heat to simmer. Cook until tender, 18 to 20 minutes. Drizzle with a little EVOO and cool. Store separately from the soup base until the soup is served, to avoid mushy buckwheat.
In a soup pot or Dutch oven, heat 2 tablespoons EVOO, a couple of turns of the pan, and add the guanciale. Brown the guanciale and then remove. Pat the beef dry and sprinkle with salt and pepper. Brown over medium-high heat in the guanciale drippings and remove. Add the garlic, onions and bay and stir and cook to soften, 8 to 10 minutes. Add the kale and wilt, and season with a few grates nutmeg. Add the tomato paste and stir until fragrant, then add the Worcestershire, the remaining beef stock, beef and guanciale. Remove the mushrooms and chop, then add the mushroom and the mushroom stock to the soup. Cook partially covered until the beef is tender, about 1 hour. Cool and store.
To serve, combine the kasha with the hot soup and serve in shallow bowls with bread and cheese curls.
Recipe courtesy of Rachael Ray