Method
Preheat oven to 350°F.
Prepare the lamb: Pat the boneless leg of lamb dry with a clean kitchen towel or paper towel to remove any moisture.
Season lamb: In a bowl, place ½ cup all-purpose flour and season generously with kosher salt and freshly ground pepper. Mix well to combine.
Cut lamb into 2-inch pieces or bite-sized pieces and toss in the flour mixture. Add more flour, salt, and pepper if needed. Coat each piece well and shake off any excess flour.
Cook bacon: Cut bacon into lardons and cook until crisp. Remove cooked bacon to a plate lined with paper towels and drain excess oil. Save the bacon fat to cook the lamb.
Brown lamb: Place seasoned lamb pieces in the Dutch oven and brown on all sides in the bacon fat. You may need to add extra virgin olive oil if you run out of fat. Watch your heat, as the flour coating can burn quickly. If this happens, wash your pot and start over with olive oil, then brown the lamb. Remove browned lamb and place in a separate bowl.
Sauté mushrooms: Add cut mushrooms and cook for about 5 minutes, or until golden brown. Remove and place in a separate bowl.
Sauté carrots: Add 1 tablespoon butter to the Dutch oven and melt. Cook carrots for 3-4 minutes, until lightly browned. Remove from pot and set aside.
Sauté onions: Add a bit of butter to the Dutch oven and sauté pearl onions for about 5 minutes, until brown patches begin to appear. Add grated garlic and cook for 30 seconds, stirring well to combine. Do not brown the garlic.
Tomato paste: Cook tomato paste for 2 minutes. Add cornstarch mixture as directed on the package and mix well into the tomato paste.
Wine: Add wine to the tomato paste, stir well to incorporate, and cook for 3-4 minutes, until the wine begins to reduce.
Beef stock: Add beef stock to the pot and stir well.
Lamb: Return lamb to the Dutch oven with the tomato paste, red wine, and beef stock mixture. Add the bouquet garni of fresh herbs, cooked bacon, 1 teaspoon kosher salt, and freshly ground pepper to taste. Stir well.
Slow cook: Bring to a simmer, then cover and transfer to the oven for 1-1½ hours, or until the lamb is tender. Add the mushrooms, onions, and carrots and mix well. Return to the oven, covered, and cook another 1-1½ hours, or until the lamb is very tender and easily falls apart.
Potatoes: While the lamb is in the oven, peel and cut potatoes into medium cube-sized pieces. Place potatoes into a pot of cold salted water with white vinegar. Cook until just barely fork-tender. Remove from heat and drain. Spread potatoes onto a baking sheet to cool.
Adjust seasonings: Check seasoning and add more salt if needed. Stir well. Add cooked potatoes and stir gently. Right before serving, mix in 1-2 tablespoons butter for an extra-rich, silky sauce.