Preheat oven to 300°F (150°C) and position the rack in the center.
Put four small (5oz.) ramekins in a baking dish that's at least as deep as the ramekins.
In a small saucepan over medium heat, bring the cream to a simmer then remove it from the heat, cover, and let cool for 10 minutes (the temperature should be no higher than 165°F or 73°C).
In the meantime, combine egg yolks, 1/4 cup sugar, and a pinch of salt in a medium bowl. Whisk until combined.
Then slowly add 1/2 cup of the warm cream to the sugar-egg-mixture while stirring constantly. Stir for 30 seconds with a whisk.
Then slowly, with a light hand stir in the remaining cream. You don't want the mixture to be frothy!
Add the vanilla extract and orange liqueur (if using) to the bowl and stir lightly until combined.
Pour the mixture through a fine sieve into a measuring cup with a spout then divide it evenly between the ramekins.
In a large pot or teakettle bring water to a boil. Transfer the baking dish with the ramekins to the oven. Then slowly pour hot water into the baking pan until the water comes about 2/3 up the sides of the ramekins. Be careful not to get any water in the ramekins.
Cover the baking pan loosely with aluminum foil.
Bake the custards for about 50-55 minutes, until the edges are set and the center is slightly jiggly. If you have an instant thermometer stick it in the center of a ramekin, it should register between 150° to 155°F (65° to 70°C).
Remove the baking pan from the oven and carefully take the ramekins out of the water bath. Let them cool at room temperature for 30 minutes then transfer them to the fridge (don't cover them). Once they are refrigerator-cold wrap them with plastic wrap. Refrigerate for at least 4 hours or up to 3 days before proceeding.
Prior to serving, sprinkle 1 tsp sugar over each custard, one at a time. Tilt and tap the ramekin to even out the layer of sugar.
Hold a torch flame 2-3 inches from the top of the custard and slowly glide it back and forth over the surface until the sugar caramelizes and turns a deep golden brown.
Allow the sugar to cool and harden for 30 to 60 seconds, and then serve immediately.