Place 18 large eggs in a pot and cover with cold water. Bring to a boil over medium-high heat.
Once the water boils, let the eggs cook for 1 minute, then reduce heat to a low simmer and cook for 11 minutes more.
Transfer the eggs to an ice water bath and let them cool for 5–10 minutes. Peel the eggs and set aside.
In a medium saucepan, combine 4½ cups white vinegar, 2¼ cups water, 3 tablespoons sugar, 1½ tablespoons salt, 3 sliced jalapeños, 6 crushed garlic cloves, 1½ cups thinly sliced red onion, 6 sprigs of fresh dill, and your optional spices (red pepper flakes, mustard seeds, coriander, dill seed, peppercorns, and cinnamon sticks).
Bring the mixture to a boil, stirring until the sugar and salt dissolve. Remove from heat and let cool slightly (warm to the touch, not hot).
Divide the peeled eggs evenly between 3 clean quart-sized jars.
Layer in the sliced jalapeños, red onion, garlic, and dill evenly among the jars.
Pour the warm brine into each jar, making sure the eggs and add-ins are fully covered. Gently tap the jars to remove air bubbles.
Seal the jars with lids and place them in the refrigerator.
Let the eggs pickle for at least 3 days before eating. For best flavor, wait 5–7 days. Enjoy within 1 month.