Preheat the oven to 475°.
Pour the milk into a saucepan over medium heat. Bring to almost boiling. (Unless you stir constantly, a skin will form on the top, but it can easily be removed.)
8 c. whole milk
In a separate bowl, beat the eggs until light. Add the sugars, flour, and salt. Beat well.
12 large eggs, 1 c. white sugar, 3/4 c. brown sugar, 1 Tbsp. all-purpose flour, 1/4 tsp. salt
Add about a cup of the hot milk to the egg mixture to temper it. Slowly add the egg mixture to the milk, whisking as you are pouring it in. Remove from the heat and add the vanilla.
1 tsp. vanilla
Immediately pour the custard mixture into a 9 x 13" metal pan. Do not use a glass pan!
Sprinkle the top of the custard with cinnamon and nutmeg, as desired.
cinnamon and nutmeg, to taste
Bake the custard for 3 minutes at 475°. Turn off the heat and let the custard sit in the oven until the oven is cool. (At least 2 hours.)
Remove the custard from the oven and refrigerate for up to a week.