Simple Tomato Soup

Ingredients

• freshly ground black pepper to taste
• 1 onion, thinly sliced
• 1 teaspoon salt, plus more to taste
• 1 cup water
• 1 tablespoon sugar
• 1 tablespoon olive oil
• 2 cans whole peeled tomatoes
• ¼ teaspoon dried oregano
• 1 pinch red pepper flakes
• 2 large garlic cloves, peeled and crushed
• ¼ teaspoon celery seed
• 1 tablespoon unsalted butter or margarine