Vegetarian "Southern-style" Collard Greens

INGREDIENTS

• 1/2 large onion, chopped
• 3 cups vegetable stock
• 1 clove garlic, finely chopped
• 2 tomatoes, seeded and chopped
• Salt and freshly ground black pepper
• 1 tablespoon butter
• 1 teaspoon red pepper flakes
• 1 pound collard greens, chopped
• 1 tablespoon olive oil