In a pot, sauté the flour in the oil until lightly golden.

Gradually add the tomato juice, starting with a small amount and stirring constantly to avoid lumps.

Using a knife, make two shallow cuts into the onion in opposite directions (about halfway through), then drop the whole onion into the pot.

Add the celery stalks if using, then season with salt and pepper.

Once the soup starts to gently boil, stir in the sugar.

Let it heat a bit longer, then add the alphabet pasta.

Stir every few minutes to prevent the pasta from sticking to the bottom.

Continue to simmer for about 15 minutes, until the pasta is tender.