This isn’t your classic beautifully layered lasagna—but it is a little more weeknight-friendly. Instead of boiling the noodles in one pot and making the sauce in another, you cook lasagna noodles directly in a mixture of milk, crème fraîche, water, and a little lemon zest, which thickens arounds the pasta as it bubbles away. (You can use sour cream in place of crème fraîche; to keep it from breaking, temper it with a little of the hot milk, then whisk in thoroughly.) The key to success is using a big enough pan—a large sauté pan or skillet with high sides or a Dutch oven that holds at least four quarts. We pop the lasagna in the broiler for a crispy top, but you can add the mozzarella in the last few minutes on the stove if you don’t want to turn the oven on.