Heat oil in a pan or kadai, add ginger, garlic, celery and saute on high for a few seconds till fragrant. Add vegetable stock, stir well, bring to a boil. Add ketchup, vinegar, sriracha, soy sauce, salt, sugar, pepper, stir and simmer for 4-5 minutes. Add cornflour slurry while stirring continuously, once it starts boiling, reduce the heat and simmer for 2-3 minutes till the sauce thickens and turns glossy. Set aside.