Slice bacon into thin strips and fry until browning and just crispy. Remove bacon and as much fat as possible from pan.
Rinse leek well and slice lengthwise in half. Place flat side down and slice into half circles.
Roughly chop spinach. Add to pan along with leek and sauté until slightly softened. Return bacon to pan and combine evenly with spinach and leeks. Allow to cool slightly.
Preheat oven to 325° and ensure rack is set to bottom setting. Place baking sheet in oven while preheating.
Arrange bacon mixture evenly in bottom of pie crust. Shred cheeses and spread evenly over top.
Whisk together eggs, milk, Dijon, salt and pepper. Place pie shell onto heated baking sheet and carefully pour custard over top.
Bake on lower rack of the oven for 35 to 40 minutes or until just set in the middle. Allow to rest for 5 minutes before slicing.
Notes
Nutrition information is based on using store bought Tenderflake pie crust, regular size.