shredded sharp cheddar or your choice
Preheat oven to 375 degrees F. Lightly grease 12 muffin tins.
Trim bread into circles. Place circles in bottom of muffin tins. Distribute the onion and shredded cheese evenly between the muffin tins.
In a medium bowl, combine milk, eggs, mustard and pepper. Divide between the muffin tins.
Bake in preheated oven for 20 minutes or until a toothpick inserted into the center of a quiche comes out clean.