Start by combining the cold water and unflavored gelatin in a small bowl. Give it a gentle stir, then set it aside for about 5 to 10 minutes to let the gelatin bloom. This is a crucial step! Blooming stabilizes the gelatin so that it incorporates seamlessly later.

In a medium bowl, whisk together the egg yolks, granulated sugar, and a pinch of salt. You want this mixture to be smooth and well combined. Take a moment to appreciate the golden color of the yolks—they’re the base for a luscious custard.

Bring the whole milk to a gentle boil in a medium saucepan over medium heat. Keep an eye on it to prevent scorching. As soon as it begins to bubble, you're ready for the next step!

Once the milk is ready, pour it in a slow, steady stream into the yolk mixture, whisking constantly. This temperature control prevents your eggs from scrambling. Ensure everything is well mixed before moving on.

Transfer the egg yolk and milk mixture back to the saucepan. You’ll want to cook it over medium heat while stirring continuously until the custard thickens slightly—about 5-7 minutes. You can test its readiness by checking if it coats the back of a spoon.

Strain the hot custard through a fine mesh strainer into a large bowl to remove any lumps. While the mixture is still warm, stir in the bloomed gelatin, pure vanilla extract, lemon juice, and lemon zest. You want to make sure the gelatin dissolves completely.

Allow the custard to cool to room temperature. This step is crucial, as incorporating the whipped cream before the custard is too hot will deflate it. Patience is key here!

In a separate mixing bowl, whip the heavy cream until you reach medium-stiff peaks. Don’t over-whip it; you want that cream to be airy and light.

Gently fold the whipped cream into the cooled custard mixture. Use a spatula and be careful not to deflate the whipped cream completely. You want to maintain that airy texture for the final dessert.

Immediately pour the mixture into parfait glasses, molds, or over cake layers. Make sure to level the tops with a spatula. Cover with plastic wrap and refrigerate for a minimum of 1 hour to allow it to set properly.