Sunny's Homemade Ketchup
Place the tomatoes, sugar, corn syrup, vinegar, allspice, peppercorns, garlic, onions and a pinch salt in a stockpot set over medium heat. Bring to a boil, and then lower to a light simmer. Use a potato masher or wooden spoon to mash down and break up the tomatoes as the mixture heats up. Cover and simmer over low heat for 45 minutes, stirring occasionally.
Uncover and cook to evaporate and thicken the sauce while stirring occasionally, 45 minutes more.
Using an immersion blender or a stand blender, blend until smooth. Pour into an airtight container and refrigerate until cool, overnight. Taste and, if needed, add 1/2 teaspoon vinegar at a time to balance the sweetness.
Blending Hot Liquids: When blending hot liquids, remove liquid from the heat and allow to cool for at least 5 minutes. Transfer liquid to a blender or food processor and fill it no more than halfway. If using a blender, release one corner of the lid; that prevents the vacuum effect that creates heat explosions. Place a towel over the top of the machine, pulse a few times, then process on high speed until smooth.