French Onion Tart - The Old Vintage Way

0 Preheat the oven to 400F.
1 Spread a thin layer of butter on a 10-inch diameter pie pan. Roll out the pie crust over it and press the bottom border to fit the pie crust.
2 Peel the onions and slice them thin by hand or with the help of a mandoline. 
3 In a wide bottom pan, add two tablespoons of olive oil over medium-high heat. Add the onion slices and cook at medium heat for about 20 minutes, stirring once in a while. You want the onions to become translucent but not brown. Lower the heat if that happens.
4 Add the two tablespoons of flour over the onions, mix well, and continue cooking for about 2 more minutes. It will look and feel thicker consistency. 
5 Add the heavy cream to the onion mixture. Mix well and cook at low heat for another 2 minutes.
6 In a bowl, whisk your eggs with salt, pepper, and nutmeg. Add the egg mixture to the onion mixture. Mix well until the eggs and onion mixture is well incorporated.
7 Drop the onion mixture into the pie crust. Smooth the top. Add the grated cheese over it, an optional step.
8 Place the pie dish over a cookie sheet. Place in the hot oven and bake for 20 minutes.  Serve hot.