Hard boil your eggs. Place them in a pot, cover with cold water, and bring to a boil. Once boiling, cover the pot, turn off the heat, and let them sit for about 10-12 minutes.

Cool and peel the eggs. Transfer them to an ice bath for about 5 minutes, then peel gently.

Pack the peeled eggs into a clean jar along with the garlic cloves and sliced onion.

Combine vinegar, water, sugar, salt, mustard seeds, and peppercorns in a saucepan. Bring to a boil over medium heat, stirring until dissolved.

Pour the hot liquid over the eggs, ensuring they are fully submerged. Seal the jar and let it cool to room temperature, then refrigerate for at least 24 hours.

In a skillet, heat olive oil over medium heat, add sliced sausage, and cook until crispy and browned (about 5-7 minutes).

Serve the pickled eggs alongside the cooked sausage, optionally with fresh baguette or crackers.