Prepare 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 the heat and let it simmer for 5 minutes to allow the flavors to meld.
Assemble the Jar:
Place the peeled hard-boiled eggs, sliced sausage, and thinly sliced onion into a clean glass jar or container with a lid.
Pickling Process:
Carefully pour the hot pickling liquid over the eggs, sausage, and onions, ensuring everything is fully submerged.
Let the jar cool to room temperature, then seal and refrigerate.
Refrigerate:
Refrigerate the jar for at least 24 hours, though the flavors will intensify the longer it sits. For best results, allow the eggs and sausage to pickle for 3-5 days before serving.
