Herbed Ham and Cheese Baked Eggs

Name: Herbed Ham and Cheese Baked Eggs
Ingredients: 2 Tbsp olive oil; 1 sweet onion, thinly sliced (about 1 1/2 cups); 1/2 tsp freshly ground black pepper; 1 1/4 tsp kosher salt, divided; 3 cloves garlic, finely chopped (1 Tbsp.); 12 large eggs; 3/4 cup sour cream; 2 tsp Dijon mustard; 4 oz Gouda cheese, shredded (1 cup); 1/4 cup chopped fresh flat-leaf parsley, plus more for topping; 3 oz Parmesan cheese, finely shredded (about 2/3 cup), divided; 8 oz deli smoked ham (8 slices), torn into pieces; 1/4 cup finely chopped fresh chives, plus more for topping