Adjust racks to top and middle positions and preheat oven to 450 degrees. Bring 1 TBSP butter (2 TBSP for 4 servings) to room temperature. Wash and dry produce.

Cut potatoes into ½-inch-thick wedges.

Toss potatoes on a baking sheet with a drizzle of oil, salt, and pepper. Roast until browned and tender, 20-25 minutes.

Meanwhile, heat a drizzle of oil in a large pan over medium heat. Add onion; season with a pinch of salt and pepper. Cook, stirring occasionally, until browned and tender, 5-7 minutes.

Add tomato paste and half the Italian Seasoning. Cook, stirring constantly, until fragrant and darkened, 30-60 seconds. TIP: If you like things spicy, add a pinch of chili flakes from your pantry.

Add marinara, stock concentrate, ½ cup water (¾ cup for 4 servings), and a pinch of sugar. Cook, stirring occasionally, until thickened, 2-3 minutes.

Stir in meatballs. Reduce heat to medium low and continue to cook until sauce is very thick and meatballs are warmed through, 2-3 minutes more.

Remove from heat; season with salt and pepper.

Once potatoes are done, remove sheet from oven.

Toast baguettes, cut sides up, directly on middle rack until golden, 2-3 minutes.

Spread softened butter onto cut sides of baguettes and season with a pinch of salt and pepper.

Fill baguettes with meatballs and sauce; sprinkle tops with mozzarella. Return to top rack until cheese melts, 2-3 minutes.

Divide meatball subs and potato wedges between plates. Serve.