Meanwhile, heat a large drizzle of olive oil in a large, preferably ovenproof, pan over medium-high heat. Add diced onion; cook, stirring, until softened, 4-6 minutes. Stir in remaining Tuscan Heat Spice, crushed tomatoes, tomato paste, ½ cup water (¾ cup for 4 servings), 1 tsp sugar (2 tsp for 4), and salt until combined. Bring to a simmer; cook until slightly thickened, 3-4 minutes. Stir in 1 TBSP butter (2 TBSP for 4) until melted. Season generously with salt and pepper.