Preheat the oven to 300 degrees Fahrenheit. In a blender or food processor, grind the dried porcini mushrooms until they are reduced to a dustlike consistency. Season the roast with salt and pepper to taste, and pat the mushroom dust onto the meaty side of the rib.

Heat a large roasting pan over two burners on medium heat and lightly coat the bottom of the pan with olive oil. Place the roast, meat side down, in the pan, and brown the meat, about 15 minutes.

Turn the roast rib side down and transfer to the oven. Roast until a meat thermometer placed in the center of the meat registers 120 degrees Fahrenheit for medium rare, about one and a half hours.

Transfer the meat to a cutting board, and let it rest, loosely covered with foil, for 15 minutes before carving.

Make the ragout while the meat is roasting. Trim the stems and slice the mushrooms into fairly thick slices.

Heat a large sauté pan over medium heat, and lightly coat the bottom of the pan with olive oil. Sauté the mushrooms, in batches, until lightly brown and crispy, five to seven minutes.

Add the onions, shallots, leeks, and garlic to the pan and slowly cook until caramelized, about 15 minutes.

Add the wine, stock, and salt and pepper to taste, and cook until the liquids reduce by half (you should have about two and a half cups of mushroom ragout at the end), about 45 minutes.

Remove the pan from the heat and stir in the lemon juice, parsley, and thyme. Adjust the seasoning with salt and pepper.

Carve the meat from the bone in thick slices, and transfer the slices to a platter or to plates.

Serve the meat with the mushroom ragout. Keep any remaining roast warm on the platter for second servings.