Preparing the Pickling Liquid
In a medium saucepan, combine the white vinegar, water, sugar, salt, black peppercorns, mustard seeds, and red pepper flakes (if using).
Bring the mixture to a boil, then reduce heat and simmer for 5 minutes to allow the flavors to meld.
Assembling the Jar
Place the peeled hard-boiled eggs, sliced sausage, and thinly sliced onion in a clean glass jar or container with a lid.
Carefully pour the hot vinegar mixture over the eggs, sausage, and onions, ensuring everything is fully submerged.
Allow the pickling liquid to cool to room temperature
