Add cornstarch slurry, stir to combine, and cook until thickened. Mix the cornstarch and water together to form a slurry in a small bowl. Sweet and Sour Sauce Directions: In a small saucepot, add the vinegar, water, and sugar. Whisk continuously until sugar is melted. water, low sodium soy sauce, rice vinegar, low sodium soy sauce and 22 more Sweet And Sour Chicken BBC green pepper, chilli flakes, tomato ketchup, cornflour, onion and 13 more How to make sweet and sour sauce. The Best Sweet and Sour Sauce, only 5 ingredients and ready in minutes! Sweet and sour sauce is something you need in your recipe arsenal. Bring vinegar mixture to a slow boil. Add the ketchup and stir until well mixed in. Homemade fakeaway sweet & sour sauce is easy to make in 10mins & tastes great - so much better than take-away or jarred sauces. Serve immediately or store for later. Place over medium heat on the stove. Add ingredients to a saucepan and bring to a boil. Vegan & easily gluten free. Not only is it delicious, it is very versatile and you can use it many different ways!