Soak lentil in 4 cups water for 4 hours. Remove from water. Pressure cook the lentil, tomatoes and celery for two whistles. Slow down the gas for 10 minutes. Close the gas. Strain the soup through a fine shift.
Heat butter on a slow heat. Saut the. Add corn flour mixed with milk and stir. Add lentil soup. Give two boils.
Remove from the gas and add salt, pepper and lemon juice. Serve warm.