Soak mustard seeds in the vinegar overnight.
Mark the tomatoes with an “X” on the base and plunge into boiling water for 30 seconds. Transfer immediately into a bowl of iced water. Drain the tomatoes, peel and chop. Set aside.
Purée the ginger and garlic in a food processor until smooth. Add the tomatoes and blend for another minute.
Heat the oil in a large saucepan unti