Zesty Spicy Pickled Eggs

1. Hard-boil the eggs: Place the eggs in a large pot and cover them with cold water. Bring the water to a rolling boil, then cover the pot and remove it from the heat. Let the eggs stand in the hot water for 10-12 minutes.
2. Prepare the pickling liquid: In a medium saucepan, combine the vinegar, water, sugar, pickling salt, red pepper flakes, turmeric powder, mustard seeds, and black peppercorns. Bring to a simmer over medium heat, stirring until the sugar and salt dissolve.
3. Peel and jar the eggs: Once the eggs are cooked, drain the hot water and immediately transfer the eggs to a bowl of ice water to stop the cooking process. Peel the eggs and place them in a clean glass jar.

4. Add the onion and jalapeño (optional): Add the sliced onion and jalapeño pepper to the jar, if desired.
5. Pour the pickling liquid over the eggs: Pour the hot pickling liquid over the eggs, filling the jar to the top.

6. Seal and refrigerate: Seal the jar tightly and refrigerate the eggs for at least 24 hours before eating. The eggs will continue to pickle and develop flavor over time.