Preheat your oven to 300°F (150°C). Place four 6-ounce ramekins in a deep baking pan.
In a medium bowl, whisk the egg yolks and 1/2 cup of sugar until the mixture is pale yellow and smooth. Do not over-whisk to avoid incorporating too much air.
In a saucepan, heat the heavy cream and salt over medium heat until it just begins to simmer around the edges. Remove from heat.
Temper the yolks: Slowly pour about one-third of the hot cream into the yolk mixture while whisking constantly. This raises the temperature of the yolks gently.
Pour the tempered yolk mixture back into the saucepan with the remaining cream. Stir in the vanilla extract.
Strain the custard mixture through a fine-mesh sieve into a clean bowl to remove any chalazae or cooked bits. This step helps create a smooth texture.
Divide the custard evenly among the four ramekins.
Carefully pour hot water into the baking pan until the water reaches halfway up the sides of the ramekins. This water bath insulates the custard.
Bake for 30 to 40 minutes, or until the edges are set but the center still has a slight jiggle when gently nudged.
Remove the ramekins from the water bath and let them cool completely on a wire rack. Then, chill them in the refrigerator for at least 4 hours, or preferably overnight.
Before serving, sprinkle an even, thin layer of the remaining 1/4 cup of sugar over the top of each chilled custard.
Use a kitchen torch to melt and caramelize the sugar until it forms a dark amber, brittle crust. Work quickly to avoid heating the custard underneath.
Let the caramelized sugar cool and harden for a few minutes before serving. Tap the top with a spoon to break the crust.
Notes
If you do not have a kitchen torch, place the sugared ramekins under a preheated broiler for 1-2 minutes, watching constantly to prevent burning.
For the smoothest custard, use whole milk or heavy cream only; do not substitute with low-fat dairy.
Make sure the water bath water is hot when you pour it into the pan to help maintain oven temperature.