Add the celery, carrot, onion and garlic to the casserole and cook, stirring, until the vegetables are barely softened, about 3 minutes.
1 rib celery, 1 large carrot, 1 large onion, 2 cloves garlic
Stir in the sage, rosemary and crushed red pepper and cook until fragrant, 2 to 3 minutes. Add the red wine and cook until it is nearly evaporated, about 10 minutes.
1 tbsp sage, 1 tbsp rosemary, 1/4 tsp red pepper flakes, 1 1/2 cups dry red wine
Add the tomato puree, chicken stock and sugar, season with pepper and bring to a boil over moderately high heat. Simmer uncovered over low heat, stirring occasionally, until the sauce is thick and reduced by half, about 45 minutes.