Silky, ultra-creamy vanilla custard flecked with espresso rests beneath a shatteringly crisp caramelized sugar top—simple, elegant, and luxurious with every spoonful.
Preheat oven to 325°F (163°C).
Whisk the egg yolks and 1/2 cup (100 g) of the granulated sugar together; set aside. Bring a small kettle or pot of water to a boil for the water bath.
In a medium saucepan over medium heat, warm the heavy cream with the espresso powder and salt just until it begins to simmer; remove from heat and stir in the vanilla.
Temper the yolks: Slowly whisk about 1/2 cup of the warm cream into the yolk mixture, whisking constantly. Then slowly pour the tempered yolk mixture back into the saucepan, whisking to combine.
Arrange ramekins in a large baking pan. Divide the custard evenly among the ramekins, filling nearly to the top.
Carefully pour hot water into the baking pan to come about 1/2 inch up the sides of the ramekins (water bath).
Bake until edges are set and centers still jiggle slightly, about 30–40 minutes depending on ramekin depth (about 35 minutes for 1-inch-deep ramekins), or until an instant-read thermometer reads 170°F (77°C).
Remove ramekins from the water bath and cool to room temperature. Cover and refrigerate at least 4 hours or overnight until thoroughly chilled.
Just before serving, sprinkle a thin, even layer of the remaining granulated sugar over each custard, fully covering the surface.
Caramelize the sugar with a kitchen torch until deep amber and crisp, or broil briefly under a hot oven broiler. Let stand 1–2 minutes to harden, then serve.