To me, the basis for a good sweet and sour sauce is to have some pineapple and some green peppers, so when I have those, I make it. They are not strictly required, though, as you can see in these recipes. Of course you can add them if you have them.

This recipe is from Yankee magazine:

Spinach Salad with Hot Maple Syrup Dressing

1/4 cup olive oil
1/4 cup pure maple syrup
1/4 cup cider vinegar
1 tablespoon crushed garlic
2 tablespoons good prepared mustard
Salt and pepper to taste
1 pound spinach, trimmed, washed, and drained
8 canned artichoke hearts, quartered

Heat the dressing ingredients and pour over the spinach and artichokes.

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Here is a meatless version of sweet and sour meatballs. It sounds like a lot of ingredients, but is worth the effort. The sauce is really good, and you might want to make more of it for this amount of meat balls. The sauce would be good over regular meatballs, too.

Sweet and Sour Meatless Balls

1/4 cup vegetable oil
1/4 cup white vinegar
1 cup apricot jam
1 cup ketchup
1/4 cup shredded onion
1 teaspoon salt
1 teaspoon dried oregano
dash hot pepper sauce

5 eggs, beaten
1 cup shredded Cheddar cheese
1/2 cup cottage cheese
1/2 cup finely chopped onion
1 cup finely chopped pecans
1 teaspoon dried basil
1/2 tablespoon salt
1/4 teaspoon sage
2 cups herb bread crumbs

To make Sweet and Sour Sauce: In a medium bowl combine the oil, vinegar, jam, ketchup, grated onion, salt, oregano and hot pepper sauce. Stir until well combined.
Preheat oven to 350 degrees F (175 degrees C). In a large bowl combine the eggs, Cheddar cheese, cottage cheese, chopped onion, pecans, basil, salt, sage and bread crumbs. Mix well and form into 2 inch balls or patties. Place them in a 9x13 inch baking dish and cover them with sweet and sour sauce. Bake at 350 degrees F (175 degrees C) for 35 to 40 minutes.

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This recipe calls for canned green beans, but of course it'd be good made with fresh.

Sweet and Sour Green Beans

1 (16 oz) can green beans
1 teaspoon corn starch
3 tablespoons sugar
3 tablespoons vinegar
1 tablespoon soy sauce
1/4 teaspoon sweet pickle relish
(2 tablespoons bacon fat and pieces)

Drain all but 1/4 cup liquid from green beans. Mix cornstarch, sugar, vinegar, soy sauce, and relish together and pour over the beans. Heat. Serve hot.