Melt butter and oil in large, heavy bottom frying pan over medium low heat. Add onions and brown sugar.
Saute' onions, stirring occasionally, until onions are very brown. This process can take up to 45 minutes, depending on the heat of your pan.
De-glaze the pan with the vinegar or wine and cook for a few minutes, scraping up the browned bits from the bottom of the pan.
Remove from heat. Let cool Before adding to eggs.
For Quiche
Meanwhile, mix eggs, milk, salt and pepper. Add grated cheese and bacon and mix well.
Saute' spinach, just until wilted, in a small pan with 1 tsp. olive oil. Drain on paper towel. Mix with the eggs.
Add onions to egg mixture. Pour into par baked crust.
Bake at 350 approximately 1 hour. If crust or eggs are getting over brown, loosely cover with aluminum foil. Let set for at least 15 minutes before cutting.
Pastry for Single Crust Pie
Cut butter into cubes. Return to fridge for a few minutes to get cold again.
Place flour, salt and shortening into food processor bowl. Add cold butter. Process until shortening forms pea sized balls.
Add water one tablespoon at a time until dough starts to clump together. Pulse, DO NOT run continuously.
Chill dough for about 1 hour. Place dough on a floured board and roll into a 12" circle. Place crust in pie tin. Crimp edges.
Par Bake Pie Crust
Cut a piece of parchment paper or waxed paper larger than the pie plate.
Place pie weights evenly on top of the crust. (If you don't have pie weights, use a bag of dried beans to hold the crust down.)
Par bake crust for about 30 minutes at 350°F / 180°C. Remove from oven. Remove pie weights or beans.
If you use beans, pour them into a quart canning jar and store for just using as pie weights.
Notes
Leftovers are good refrigerated for 3-4 days.To Reheat, briefly in microwave for about 60 seconds.Do not freeze leftovers.
When you are cooking bacon for your family, cook a few extra pieces and freeze them for use in future dishes, like this quiche.
When you buy a bag of spinach, wilt the entire bag. Then freeze any leftovers for use in future dishes, like this quiche.
Place a rimmed baking sheet under quiche to catch any drips, so it doesn't make your oven a mess.
If you don't have pie weights to par bake the crust, use a bag of dried beans spread evenly over crust.
Reserve the beans specifically for pie weights in the future. Store in a quart mason jar.
You want to quiche to jiggle slightly (reminiscent of Jello brand gelatin) in the center when you take it out of the oven. It will continue to cook once it comes out of the oven.
When you remove quiche from the oven, tent it with aluminum foil. Let rest for at least 15 minutes.