Step 1

Heat the oven to 325°F. Line the bottom of a 9x13-inch baking pan with a small kitchen towel (fold as needed so it lies completely flat). Lightly coat 8 (6-ounce ramekins) with cooking spray and place on the baking pan. Bring about 6 1/2 cups water to a boil in a kettle or saucepan, then turn off the heat.

Step 2

Whisk 4 large egg yolks, 1 cup of the granulated sugar, 3/4 cup whole milk, the finely grated zest of 1/2 medium lemon, 1/2 cup lemon juice, 2 tablespoons melted unsalted butter, 1/2 teaspoon vanilla extract, and 1/4 teaspoon kosher salt together in a large bowl. Whisk in 1/3 cup all-purpose flour until smooth and free of clumps.

Step 3

Whisk 4 large egg whites in a medium bowl until foamy. Add the remaining 1 tablespoon granulated sugar and whisk until soft peaks form, 2 1/2 to 5 minutes. (Alternatively, mix with an electric hand mixer on medium speed.)

Step 4

Transfer half of the egg white mixture into the egg yolk mixture and gently whisk together until just combined. Add the remaining egg white mixture and gently whisk until just combined; the mixture will be smooth and fluffy. Evenly divide the batter between the ramekins (about 2/3 cup each; the ramekins will be full).

Step 5

Pull the oven rack out about halfway and place the baking pan on it. Carefully and slowly pour enough of the hot water into the pan (do not let any water splash into the ramekins) so that it comes about halfway up the sides of the ramekins. Make sure the towel is completely soaked. Slowly push the oven rack back in.

Step 6

Bake until the top of each pudding cake is puffy and set and the cake begins to slightly pull away from the ramekins, 32 to 34 minutes.

Step 7

Remove the baking pan from the oven. Using tongs or oven mitts, carefully transfer the pudding cakes to a wire rack. Let cool for at least 15 minutes before serving. Serve dusted with powdered sugar and freshly grated lemon zest or topped with whipped cream if desired.