Mini quiches with ham and caramelized onions - Le Coup de Grâce

Ingredients

• 1 small yellow onion, finely chopped
• Olive oil
• 1 tablespoon balsamic vinegar
• 2 tablespoons butter
• 227 g white mushrooms, thinly sliced
• 12 eggs
• 1 cup grated sharp cheddar cheese
• 2/3 cup smoked ham, diced
• 1/3 cup milk
• 2 tablespoons chopped fresh parsley
• 1/2 teaspoon Italian spices
• 1/2 teaspoon baking powder
• Salt and pepper from the mill