Soak Kashmiri red chillies in hot water for about 1-2 hours. After that make a fine paste of the chillies using the same water.
Take a non-stick pan, switch on the gas and add all the oil, once oil becomes hot add finely chopped garlic and cook it for around 20 seconds.
Then add ginger and again cook it for another 30 seconds on medium to low flame.
Now add finely chopped celery stems and mix well, cook everything for about 1 minute.
Now add Kashmiri red chilli paste and mix well, cook the mixture for about 2-4 minutes on low flame.
Now add soy sauce, salt, ketchup and mix well, cook the sauce again for 2 minutes and add around 1/2 cup of water to adjust the consistency of the sauce.
After sauce becomes thick and leaves oil from the sides, say after 5-8 minutes, switch off the gas and add vinegar, mix well.
Transfer the sauce into a sterilised glass jar and store it in the fridge for 7-8 days. Enjoy the homemade Schezwan.
