Savory Sourdough Quiche

Name: Savory Sourdough Quiche
Prep time: 15 min
Cook time: 40 min
Total time: 55 min
Cuisine: American, French
Ingredients: 1 sourdough pie crust; 1 tablespoon butter or olive oil (for sautéing); 3 medium onions (diced); 2 cloves garlic (minced); 300 grams fresh asparagus (trimmed and cut into pieces); salt and black pepper (to taste); 6 large eggs; 120 - 240 grams cooking cream or milk; 1 tablespoon mustard (I like Dijon); Fresh parsley for garnish (optional)