Blanch and skin tomatoes then roughly chop. In a bowl, mix tomatoes with onions. Sprinkle with pickling salt and set overnight.
Rinse and drain tomatoes mixture; place in a large pot and add cider vinegar. Bring to a boil.
Meanwhile, mix dry mustard with vinegar and add, along with curry, sugar and jalapeños, to tomato and onion mixture. Simmer to thicker consistency, about 45 minutes; place in warm, sterilized jars and process in 325°F (160°C) oven for 20-25 minutes. Makes 5 to 6 jars.
Tip: to blanch tomatoes, place tomatoes in a large bowl and cover with just boiled water; let stand for a minute. Using a slotted spoon, transfer tomatoes to a bowl or sink filled with ice water until cool. The skins should slip off easily.