Preheat oven to 325°F (163°C).

Place 4-6 ramekins in a deep baking dish.

In a saucepan over medium heat, warm the heavy cream, lemon zest, and vanilla extract until hot but not boiling.

Remove from heat and let sit for 5 minutes to infuse flavor.

In a mixing bowl, whisk together egg yolks, sugar, salt, and lemon juice until pale and smooth.

Slowly pour a little of the warm cream into the egg mixture, whisking constantly.

Gradually add the rest while whisking to prevent scrambling.

Strain the mixture through a fine-mesh sieve into ramekins.

Pour hot water into the baking dish until it reaches halfway up the ramekins.

Bake for 30-35 minutes, or until the center is set but still slightly jiggly.

Let cool, then refrigerate for at least 3 hours.

Before serving, sprinkle a thin, even layer of sugar over each custard.

Use a kitchen torch to caramelize the sugar, or place under a broiler for 1-2 minutes.

Let the sugar harden for 1 minute, then crack with a spoon and enjoy!