Using a medium saucepan over medium heat, saute onion in the oil for 4-5 minutes, until soft and translucent. Add the garlic and cook another 1-2 minutes. Pour in the vinegars, your choice of sweetener, and salt. Bring to a boil.
Add both the tomato puree and the paste and return to a boil. Stir in the spices. Turn down the heat slightly and cook until the sauce thickens and reduces, about 15 to 20 minutes. Taste and adjust the seasonings.
Let cool a bit, and if you have an immersion blender, blend the sauce until it’s smooth. Otherwise, put it in a blender and blend until it’s smooth.
Pour the ketchup into a mason jar or other airtight container and store in the refrigerator. This will keep for 2-3 weeks.