Start by preheating your oven to 325°F (162°C). This temperature ensures a gentle bake that keeps the custard velvety smooth.

Next, place your ramekins in a large baking dish. This allows for a water bath, which helps regulate the temperature and prevents the custard from curdling. Make sure to leave some space between them.

In a saucepan, combine the heavy whipping cream and half of the granulated sugar (about 1/4 cup). Stir gently, and heat over medium heat until it just begins to simmer. You want to avoid boiling—keep a keen eye on this stage!

While the cream heats, take a medium-sized bowl and whisk together the egg yolks, the remaining sugar, and salt until the mixture is pale and slightly thickened. This step is crucial; it helps create that silky texture.

Once the cream is heated, slowly pour it into the egg yolk mixture, whisking constantly. This step is essential—it's called tempering. You don’t want to scramble the eggs!

Stir in the vanilla extract, dark rum, espresso powder, and lemon zest. This combination of flavors elevates the dish from ordinary to extraordinary.

Carefully pour the mixture into each ramekin, filling them about three-quarters full.

Pour hot water into the baking dish until it reaches halfway up the sides of the ramekins. This water bath is what keeps the custards from overheating.

Place the baking dish in the preheated oven and bake for about 40-45 minutes. The edges should be set, while the center remains slightly jiggly.

Once baked, remove the ramekins from the water bath and let them cool. Cool to room temperature, then refrigerate for at least four hours—or overnight if you have the patience!

When you’re ready to serve, sprinkle a thin layer of granulated sugar on the top of each custard.

Using a kitchen torch, carefully caramelize the sugar until you achieve that beautiful golden, glass-like crust. If you don’t have a torch, a broiler will work; just watch it closely to prevent burning.