Gather about 3 lbs of leeks and remove the dark green parts (discard, add to compost pile, or clean well and use to make a stock). Slice leeks in half and remove the root end. Hold under running water while ‘flipping’ the leaves of the leek with your thumb. Any dirt should wash away. Cut into 1/4″ slices.
Alternatively, slice the leeks and let swim in a big bowl of cold water. Lift out the leeks after the dirt/sand has settled to the bottom of the bowl and drain well in colander. DO NOT POUR EVERYTHING THROUGH THE STRAINER. You will essentially shower your clean leeks with the dirt you tried to wash off.
Pile the leeks into a large saute pan and add a couple of tablespoons of butter and/or olive oil. Place over medium heat and let things gradually begin to heat up. You want a gentle cooking, not a furious sizzle, so once the leeks begin to glisten and cook down, turn the heat to low. Season them with salt and pepper.
You want the leeks to continue to wilt and not burn or brown. Allow this gorgeous mixture to cook over low heat for about 30 minutes, stirring frequently (every 5 minutes or so). Once the leeks cook down by about half and are all sweet (you must taste them – you MUST!) and luscious and soft, turn off the heat and let them cool.
If your pie shell is ready and your oven is preheated to 400°, you can go right ahead and make the tart. Or you can store the cooked leeks in a covered container in the fridge for about a week or so.
Load up your unbaked pie shell (homemade is great, but storebought works just fine) with all of the cooked leeks. In the photos above, I did a double batch of both pie dough and leeks – this made a 9″ x 1″ high tart and 2 – 6″ x 2″ high mini tarts. If there is any liquid remaining, do NOT put that in the shell.
In a bowl, beat 1/2 cup heavy cream and 2 eggs with a fork or whisk until combined. Season with salt and pepper and pour over the leeks. The pie shell will be quite full. Press down with a rubber scraper and wiggle the leeks a bit to get into all the nooks and crannies (Now I’m craving English muffins. Damn.).
Bake the tart(s) in a preheated 400° oven for 20-30 minutes or until golden brown and knife inserted in center comes out clean of goo. Let it rest at least 10 minutes on a wire cooling rack, then dive in and enjoy all your hard work.