serves: 4 cups of filling
I love custards-when they are properly baked, that is, so each spoonful feels like velvet and truly melts on the tongue, releasing all its flavors. This is one of the most basic pleasures of eating, one that my family enjoys and that I want to share with you. For uniform baking, I recommend that you use identical molds to bake up a batch if possible. If you don't have any, I encourage you to buy a set of inexpensive 1/2-cup ceramic molds-get eight or a dozen; either small shallow soufflé shape or the taller traditional custard cup is fine. You'll use them forever, I hope.
For the Ramekins
2 tablespoons soft butter
For the Mushroom Filling
4 tablespoons soft butter
1½ cups leek, washed and finely chopped
1 teaspoon salt
3 fresh sage leaves, finely chopped
1 garlic clove, peeled and minced
2½ cups cremini mushrooms, thinly sliced
½ teaspoon dried porcini powder, pulverized in spice grinder, or by hand
freshly ground black pepper
1 tablespoon Italian parsley, freshly chopped
For the Custard
4 large eggs
2 cups milk
Preheat the oven to 375 degrees and set a rack in the center.
Butter the insides of the ramekins or custard cups generously. Set the ramekins in the empty baking dish.
Put the 4 tablespoons of butter in a medium skillet and set over medium heat. When the butter is starting to foam, stir in the leeks and 1/4 teaspoon salt and cook for 3 minutes or so until the leeks are sizzling and softening. Stir in the chopped sage, and cook a couple minutes more; lower the heat if necessary so the leeks don't brown. Push the leeks aside to clear a space in the middle of the pan and drop in the minced garlic. Stir the garlic in the hot spot for a minute, then stir in with the leeks.
Now drop in all the mushrooms, sprinkle on another 1/4 teaspoon salt, the porcini powder, grinds of pepper. Raise the heat slightly and cook for a minute or 2, stirring frequently. Cover the pan and cook for 3 minutes or so, shaking the pan occasionally; so the mushrooms release most of their liquid. Uncover the pan and cook rapidly to evaporate the juices, stirring often, just until the mushrooms have started to caramelize and stick in the pan. Remove the pan from the heat, stir in the chopped parsley and let the mushrooms cool a bit.
Beat the eggs and the remaining salt with a whisk in a large mixing bowl, until smooth. Pour in the milk, whisking steadily to blend well. Scrape in the cooked mushroom mixture and stir gently until every bit is dispersed. Pour or ladle the custard into the prepared cups, filling them evenly.
Pour very warm (not boiling) water into the baking pan, to come about 1/2 way up the side of the cups, and carefully move it onto the oven rack. Or put the pan into the oven first and then pour in the warm water.
Bake for about 10 minutes and check how the custard is cooking: shake the pan or a cup gently: if the custard is still loose, as is likely, the surface will slosh a bit. After 15 minutes, the custards should have started start to set around the sides - this part will wobble, like Jell-O, though the center may still be sloshing. Check the custards every 2 to 3 minutes now. When the tops are all set (just wobbling) lay two fingers on them and press gently. At first, there may be liquid under the surface - cook slightly longer until the custard feels set but soft, and moves beneath your fingers.
Now they are done. Remove the pan from the oven to a stable surface. Lift out the cups with dry towels (remove some of the hot water from the pan to make this job easier) and let them rest on a wire rack to cool briefly. Serve warm.