Sprinkle the gelatin over the cold water in a small bowl and let it sit 5 minutes to bloom.

Combine 1 cup heavy cream and 1 cup whole milk in a medium saucepan over medium heat and heat until small bubbles form around the edges, about 160°F, without boiling.

Whisk together the egg yolks and 1/2 cup granulated sugar in a medium bowl until pale yellow and slightly thickened, about 2–3 minutes.

Slowly pour about 1/4 of the hot cream mixture into the egg yolk mixture while whisking constantly, then gradually whisk in the remaining cream to temper the eggs.

Return the mixture to the saucepan and cook over medium-low heat, stirring constantly, until it reaches 160°F or coats the back of a spoon, about 8–10 minutes.

Strain the custard through a fine mesh strainer into a clean bowl, stir in the bloomed gelatin and vanilla extract until dissolved, and cool to room temperature, about 15–20 minutes.

In a large mixing bowl, whip the remaining 1 cup heavy cream with the remaining 1/4 cup sugar until stiff peaks form, about 2 minutes.

Gently fold the whipped cream into the cooled custard with a rubber spatula until uniform and no white streaks remain.

Divide the mixture into individual ramekins or a 1-quart mold and refrigerate for at least 4 hours or overnight until set.