Panggang Brunch Telur dan Croissant

Bahan-bahan (9 porsi)

• 2 tablespoons olive oil
• 1 large yellow onion, sliced thinly
• 2 1/2 cups diced ham
• 2 -3 ounces fresh baby spinach
• 1 cup shredded cheese (I used a Swiss/Gruyere mix)
• 12 eggs
• 1/2 cup milk
• 1 tablespoon Dijon mustard
• 1 teaspoon salt
• pepper to taste
• 5 -6 mini croissants, torn into small pieces (or 3-4 large size)