2medium leeks, about 1 lb, white and light green parts only
1/4lbthick cut bacon
Freshly ground black pepper
6ouncesGruyère cheese, coarsely grated
Preheat the oven to 350°F and thoroughly grease a 9 x 9-inch baking dish.
Separate the English muffin halves, then cut them into 3/4-inch cubes. Arrange the cubes in a single layer on a baking sheet and bake until very lightly toasted, 10 to 12 minutes. Remove from the oven and set aside.
Cut the leeks in half lengthwise, separate the layers and rinse thoroughly to remove any dirt that's trapped between them. Pat dry, then slice crosswise into 1/4-inch thick pieces.
Cut the bacon into 1/4-inch pieces and begin frying in a large skillet over medium heat. As soon as the bacon begins to render some of its fat, add the onion and continue cooking, stirring frequently, until the onion is soft and translucent, about 3 minutes.
If necessary, drain all but 1 tablespoon of the bacon fat from the pan, then add the leeks and sauté the mixture until they soften, 3 to 5 minutes. Remove from the heat and allow to cool.
Whisk the eggs and milk together in a large bowl. Add the salt and a few grinds of black pepper, whisk again and set aside.
To assemble the strata, layer half of the English muffin cubes in the bottom of the prepared baking dish. Scatter half of the bacon-leek mixture on top, then cover with 1/2 of the grated Gruyère. Repeat the process with the remaining ingredients, then carefully pour the egg mixture evenly over the entire dish.
Cover tightly and refrigerate for at least 4 hours, preferably overnight.
To bake, position a rack in the middle of the oven and preheat oven to 325°F. Uncover the strata and bake until puffed and golden and the edges begin to pull away from the sides of the dish, 45 to 55 minutes.