Cut the Lamb Shoulder into generous 1½–2 inch pieces and pat dry; season all over with Salt and freshly ground Black Pepper.
Heat a large, heavy-bottomed casserole over medium-high heat and add a splash of Olive Oil and a knob of Butter. Brown the lamb in batches so it gets a deep crust without overcrowding, then transfer the browned pieces to a plate.
Reduce the heat to medium and add the chopped Onion and crushed Garlic to the pot; cook until softened and starting to color, about 5–7 minutes.
Sprinkle in the Plain Flour and stir for 1–2 minutes to cook out the raw taste, then stir in the Tomato Paste and chopped Tomato and cook briefly to meld the flavors.
Pour in the Dry White Wine to deglaze, scraping up any browned bits from the bottom of the pan, then return the lamb and any accumulated juices to the pot.
Add enough Stock to just cover the meat, drop in the Bouquet Garni, bring to a gentle simmer, cover partially and braise on low heat (or in a 160°C/320°F oven) until the lamb is nearly tender, about 1 to 1¼ hours.
Add the peeled and chopped Carrot, diced Turnip and halved New Potatoes to the pot, cover and continue to simmer until the root vegetables are almost cooked through, about 20–30 minutes more.
Stir in the peeled Pearl Onions, trimmed Green Beans and Peas, and cook just until the beans and peas are bright and tender, about 6–8 minutes.
Taste and adjust seasoning with more salt and pepper if needed. Remove the [Bouquet Garni], then swirl in a little extra Butter for sheen and richness and sprinkle with chopped Flat-Leaf Parsley before serving.
Ladle the navarin into bowls with plenty of sauce and vegetables, and serve hot with crusty bread to soak up the juices.
