I've taken all of the important and the subtle nuances of onions and layered them into this savory pie. It's a cross between a classic southern tomato pie, a buttermilk pie and an onion tart. The caramelized onions start in a slow cooker with sherry and thyme (if you feel fancy). Overnight, the translucent petals of white, yellow, red and sweet onions melt, become bronzed and bathe in their own juices to produce a cohesive tangle of skins that are baked under a mayonnaise and Parmesan crust inside of a buttery pie shell and garnished with a little bit of fresh chopped chives. It's super fantastic.
Transfer all of the thinly sliced onions to the slow cooker — the slow cooker should be half to three-quarters full.
Cook for 5 hours on HIGH or 10 hours on LOW.
Stir occasionally, if possible — this will help them cook more evenly, but is not necessary.
After 5-10 hours, the onions will be golden-brown and soft, and they will have released a lot of liquid. Remove onions to a large bowl and let cool.
If you like onions with a deeper color, continue cooking for another 3 to 5 hours on LOW. Leave the lid ajar so the liquid can evaporate. Check every hour and stop cooking whenever the onions look and taste good.
Preheat oven to 375 degrees F.
In a large bowl, mix 3 cups of the cooled onions with yogurt, hot sauce, eggs and salt and pepper. Make sure all ingredients are well blended and then pour into 1 pie shell.
In a small bowl, mix grated cheese, mayonnaise, salt and pepper until well-blended. Spoon mixture on top of the onion mixture in the pie shell.
To prevent burning or over-browning the pie crust, cover the crust with aluminum foil. Bake in the preheated oven for 35 minutes.
Remove foil from the pie crust and bake for an additional 15 minutes, or until golden brown on top. Garnish with chives, if using. Let cool for a few minutes to settle before slicing.
Pie can be served hot, warm, or at room temperature.