Prep the lamb. Pat the lamb dry with paper towels, then season all over with salt and pepper. Dry meat browns better, which boosts flavor.

Sear in batches. Heat olive oil in a large skillet over medium-high. Sear the lamb in batches, 2–3 minutes per side, until browned. Don’t crowd the pan. Transfer to the slow cooker as you go.

Sauté the aromatics. In the same pan, add onion, celery, and a pinch of salt. Cook 3–4 minutes until softened. Stir in garlic and tomato paste; cook 1 minute until fragrant and slightly darkened.

Deglaze and thicken. Sprinkle flour over the veggies and stir. Pour in the red wine, scraping up browned bits. Simmer 1–2 minutes to reduce slightly; it should look glossy and thick.

Load the slow cooker. Add carrots, baby potatoes, and the wine mixture to the slow cooker. Pour in the stock. Add rosemary, thyme, and bay leaves. Stir and taste the liquid; adjust salt if needed.

Cook low and slow. Cover and cook on Low for 7–8 hours or High for 4–5 hours, until the lamb is fork-tender and the potatoes are soft.

Finish with brightness. In the last 20 minutes, stir in the peas. Remove the herb stems and bay leaves. Add zest of half a lemon and 1–2 teaspoons lemon juice to lift the flavors.

Adjust consistency. If the stew is too thin, mix 1 tablespoon cornstarch with 1 tablespoon cold water and stir it in. Cook 10 minutes more to thicken. If it’s too thick, splash in more stock.

Garnish and serve. Top with chopped parsley. Serve with crusty bread, buttered noodles, or a simple green salad.