Cut 2 1/2 pounds peeled small red onions into 6 to 8 wedges or slice into 1/4-inch slices. In a large pan, combine 4 1/2 cups red or white wine vinegar (my family likes the wedges in red wine vinegar and the slices in white wine vinegar - do not use distilled white vinegar), 1/2 cup sugar and 1 teaspoon whole black peppercorns. Over medium-low heat, gradually heat the mixture, stirring constantly, until the sugar is completely dissolved.
Increase the heat to medium-high and bring the syrup to a boil. Reduce the heat and simmer for 5 minutes. Add the onion wedges or slices and heat for 5 minutes. Remove the pan from the heat. Pack the hot onions into hot pint jars (makes enough for about 4 pint jars), leaving 1/2-inch headspace. Using a bubble freer or plastic knife, remove any air bubbles. If necessary, add more syrup to maintain the headspace. Wipe the jar rims and threads with a clean, damp cloth. Cover with hot lids and apply screw rings.
Process jars in a 180 to 185 degrees F water bath for 30 minutes. Use the sliced red onions in white wine vinegar (or red wine vinegar) on salads, as part of an antipasto platter (wedges work well for this too) hamburgers and roast beef sandwiches. Sometimes the simplest things in life are the very best things.
NOTES: When preserving foods it is imparative to use hot jars when adding hot liquid. I usually wash and dry them in the dishwasher and try timing the end of the cycle near the time I will be filling the jars. Heat your lids in a small pan of water that has been brought to a simmer and removed from the heat. Cover the pan and allow the lids to heat for at least 10 minutes. Keep the lids hot until needed.
Be sure to fill the jars all the way up with liquid to the given headspace required for keeping your food preserved at its best. Foods can turn brown/ go bad if the jars are not filled properly.
To process jars make sure that you use a candy or canning thermometer to check the water temperature in the water bath. Process the jars at the temperature and for the length of time specified in the recipe. Do not shorten processing time, or any bacteria in the jars may not be killed and the lids may not seal properly.
When you remove the jars from the water be careful not to tip the jars. Place the jars on a wire rack leaving at least an inch between jars for air circulation to cool. Use a clean towel to carefully blot any standing water from the tops of the jars. Allow the jars to cool for 12 to 24 hours. Listen for the popping sound made by the lids as jars cool and seal. After 24 hours check all seals to make sure that they are sealed. Press down in the center of the lid. If the lid remains down, the jar is sealed and safe for storage. If the center of the lid pops up, the jar is not sealed and you can then store the jar in the refrigerator and use the contents within a month. Or you can empty the contents into a pan, heat and reprocess in a clean jar with a new lid.
Remove the screw rings and lable and date the jars for storage. Store jars in a cool, dry place.