Generally, you’ll want to use the lighter parts of the leek because that is where the flavor is.
The darker parts are great for stock, no need to waste any part.
As you will discover, between the layers, there may be flecks of dirt. Sometimes even clumps.
An easy way to remove the dirt is to soak the sliced leeks in a bowl of tepid water for about 10 minutes, stirring occasionally. Most of the dirt will fall to the bottom. Remove them with tongs or with your hands careful not to stir up the dirt that falls to the bottom.
In the meantime, cut up the bread in 1 inch cubes and toast in the oven on a sheet pan for 15- 20 mins until brown and dry.
Once the bread cubes are in the oven, make the egg mixture.
Crack three large eggs in a medium sized bowl.
Whisk well and add milk, half and half …..and whisk some more.
You may be tempted to use all half and half, or heavy cream. I’ve done this, and it was WAY too rich.
Add salt, thyme, chives, nutmeg and white pepper.
Grate some gouda.
By now your leeks should be tender …
and your toasty bread cubes.
Place your bread in a large bowl and add the leeks.
Grease your baking dishes. You could do this in one large deep 9 x 13 baking dish or several smaller ones. I have even done them in small individual sized ramekins as well.
Layer cheese and bread leak mixture. Pour enough custard over the top while gently pressing down the bread so it soaks in the custard. Let sit 10 minutes and pour the remaining custard allowing some of the bread cubes to protrude.
Top with the remaining cheese, and a sprinkling of salt.