Bear with me on this one.
All kinds of ketchup are sweet-and-sour sauces with a fruit base. We're just used to the tomato one. When you buy ketchup in the store, almost all brands identify it as Tomato Ketchup. Ketchup has a very long history that I'm not going into. Suffice it to say, the tomato version has only existed for two or three hundred years.
So, this one is based on strawberries. You can use a variety of vinegars for the sour part, but cider vinegar seems to make the most sense. Definitely taste and adjust the vinegar-sugar balance near the end. It will depend entirely upon the sweetness of the berries.
*1 lb fresh or frozen strawberries
1/2 C diced onion
1/4 C cider vinegar
1/4 C light brown sugar
1 bay leaf
1 cinnamon stick
salt, white pepper, and paprika to taste
1. Place strawberries and onion in a medium saucepan. Simmer over medium-low heat until berries and onion are cooked soft and most of the water has evaporated, about 20 minutes. Stir periodically.
2. Purée softened berry mixture in the blender. Return to saucepan and add remaining ingredients. If you don't think you'll be able to find the leaf and stick, put them in a cheesecloth pouch first. Stir and continue to simmer for half an hour, until mixture is thick and has absorbed the herbs. Taste and adjust levels of seasoning, vinegar, or sugar. Discard bay leaf and cinnamon stick, and refrigerate until ready to use.
Makes about 1 cup
So, what do you do with it? You could use it to dip apple or banana chips. Serve it on a salad as a strawberry vinaigrette. I made some bizarre, mediterranean-inspired tacos and used it instead of salsa: