01 - Preheat oven to 300°F. Arrange four 6-oz ramekins in a deep baking dish.
02 - Combine milk, heavy cream, and vanilla bean seeds plus pod in a medium saucepan. Warm over medium heat until just simmering, then remove from heat. If using vanilla extract, stir it in now.
03 - In a mixing bowl, whisk egg yolks, sugar, and salt until pale and slightly thickened.
04 - Gradually add hot milk mixture to egg yolks, whisking constantly. Discard the vanilla pod if used.
05 - Pass the combined mixture through a fine mesh sieve into a large bowl or measuring cup for a smooth texture.
06 - Divide the custard evenly among the prepared ramekins.
07 - Fill the baking dish with hot water until it reaches halfway up the sides of the ramekins.
08 - Bake for 30 to 35 minutes, until the custard is set but slightly jiggly in the center.
09 - Remove ramekins from water bath carefully. Let cool to room temperature, then cover and refrigerate at least 2 hours before serving.