Heat oil in a pressure cooker, add onion, garlic cloves and ginger, and sauté for 2 minutes until it shrinks slightly.
Add tomatoes and mix them well
Add roughly chopped beetroot, black pepper powder and salt, and cook for 2 minutes until it softens slightly.
Add 2 cups of water and pressure cook on a high flame for one whistle, then turn the flame to low. Cook the vegetables for 5 minutes on a low flame, then turn off the flame.
Let it cool down completely. Strain the vegetables through a strainer and let them cool down completely. Keep the vegetable stock. Do not discard it.
Transfer the cooked vegetables into a blender and blend them to a smooth puree.
Transfer the puree to the strainer again and strain it through a fine strainer.
Transfer the strained puree to a kadhai or pan. Add the reserved vegetable stock and mix it well.
Add one tablespoon of butter and mix it well. Adjust the consistency and seasoning as per your taste.
Once the soup comes to a boil, turn off the flame.
Tomato beetroot soup is ready to serve; garnish the soup with cream (optional) and coriander leaves and serve it hot.