Heat the heavy cream in a pot over low-medium heat.
In a bowl, whisk together the egg yolks, sugar, and vanilla.
Slowly pour the warm cream over the egg mixture, whisking constantly. Strain through a fine sieve to remove air bubbles and any bits of cooked egg.
Place the ramekins in a baking pan. Pour the custard into the ramekins, then fill the baking pan halfway with boiling water.
Bake at 350°F/180°C for 35 minutes — the centers should still jiggle slightly when done. Let cool at room temperature, then cover and refrigerate for at least 4 hours (overnight preferred).
Just before serving, sprinkle a thin, even layer of sugar on top of each custard and caramelize with a kitchen blowtorch, or place under the broiler. Repeat 1–2 more times for a thicker, crackly crust. Optional: Freeze for 30–45 minutes before serving for extra-firm custard.