• Heat broiler to high. Wash and dry produce. • Dice potatoes into 1/2-inch pieces. Strip thyme leaves from stems; roughly chop leaves. Trim, peel, and halve carrot lengthwise; slice crosswise into 1/4-inch-thick half-moons. Finely dice celery. Halve, peel, and finely chop onion. Peel and mince garlic.

• Place potatoes in a medium pot with enough salted water to cover by 2 inches. Bring to a boil and cook until tender, 15-20 minutes. • Drain and return potatoes to pot. Mash with sour cream, 1 TBSP butter (2 TBSP for 4 servings), and 1 tsp chopped thyme until smooth and creamy, adding splashes of water as needed. Season generously with salt and pepper. • Cover to keep warm.

• Meanwhile, heat a drizzle of oil in a medium, preferably ovenproof, pan (use a large, preferably ovenproof, pan for 4 servings) over medium-high heat. Add carrot; season with salt and pepper. Cook, stirring, until slightly softened, 2-3 minutes. • Add celery, onion, and a large drizzle of oil; season with salt and pepper. Cook, stirring, until veggies are just tender, 5-7 minutes. TIP: If veggies begin to brown too quickly, add a splash of water. • Stir in garlic and 2 tsp chopped thyme; cook until fragrant, 30 seconds.

• Remove sausage from casing; discard casing. • Add sausage to pan with veggies. Cook, breaking up meat into pieces, until browned and cooked through, 4-6 minutes. • Add tomato paste and flour; cook, stirring, until thoroughly combined, 1 minute. Pat chicken dry with paper towels and season with salt and pepper. Simply cook through this step as instructed, swapping in chicken (no need to break up into pieces!) or chicken sausage (no need to remove casing—there isn't any!) for pork sausage.

• Gradually stir 1/2 cup water (3/4 cup for 4 servings) into pan with sausage mixture. • Stir in stock concentrate and bring to a boil. Cook until mixture is very thick, 1-2 minutes. • Taste and season with salt and pepper. TIP: If your pan isn’t ovenproof, transfer filling now to a baking dish.

• Top sausage filling with an even layer of mashed potatoes, leaving a 1-inch border around edge of pan. Evenly sprinkle mashed potatoes with cheddar. Broil until browned, 3-4 minutes. TIP: Watch carefully to avoid burning. • Let rest at least 5 minutes, then divide between plates and serve.