Dissolve the cornstarch into the water, then add the ketchup, soya sauce and apple vinegar.
Put in a small pan and cook over low heat, stirring until it thickens.
Add minced ginger, black pepper and serve at room temperature.
Sweet and Sour Sauce
2 tbsp ketchup
2 tbsp soya sauce
1 tbsp apple vinegar
1 tbsp cornstarch
30ml water
1 tsp minced ginger
1 pinch of black pepper, ground