Measure the half & half in a 2-cup glass liquid measuring cup.
Using the tip of a sharp knife, split the vanilla bean lengthwise down the middle, then scoop out the seeds with the narrow part of a spoon. Add the seeds and vanilla bean pieces to the half & half and heat the mixture in the microwave until very hot, 2 to 3 minutes.
Cover with a kitchen towel and let the mixture steep for 30 minutes, or up to 2 hours. The longer the half & half and the vanilla bean and seeds steep, the more pronounced the vanilla flavor.
Make sure your oven rack is in the middle position and pre-heat the oven to 325°F.
Place 4 6-ounce (3/4-cup) ramekins in a baking pan with 2-inch high sides.
In a medium heavy bottomed saucepan, whisk the yolks, sugar, and salt until well blended.
Uncover the half & half slowly pour it in, vanilla bean pieces and all, into the yolk mixture, whisking all the while. Whisk until well blended.
Cook over medium-low heat, stirring constantly with a silicone spatula until thickened and it coats the back the spatula (170-172°F on an instant read or candy thermometer), about 4 to 5 minutes (mine took longer, but I may have had the heat lower).
Remove the pan from the heat and fish out the vanilla bean pieces, scraping any custard from the pod back into the custard. (If using vanilla extract or paste instead, stir it in.)
Pour the custard into the ramekins, being careful not to slop it all over the place.
Carefully fill the baking pan with hot tap water coming halfway up the sides of the ramekins and cover the pan loosely with foil.
Bake until the pots de crème wiggle like Jell-o when nudged, about 35 to 45 minutes, depending on thickness of the ramekin walls.
Remove the baking pan from the oven and transfer the ramekins to a wire cooling rack to cool completely.
Once cooled, cover with plastic wrap and refrigerate at least 4 hours, or up to 2 days before serving.