Preheat oven to 170C/Gas Mark 3.
Place the milk and vanilla bean in a saucepan, over medium flame, bring to boil. In separate bowl, beat the yolks with sugar. Pour the hot vanilla-milk into the yolk/sugar mixture, and stir.
To bake the pot de creme: Bring a pot of water to boil. Fill ramekins to 3/4 full with custard mixture; cover the ramekin with aluminium foil. Line a hotel pan or sheet pan with parchment paper, place ramekins in it, slide the pan into the oven and fill the pan with the boiling water, to halfway up the sides if the ramekins. Check custard occasionally to make sure the hot water doesn't boil, if it boils at any point, turn the oven down immediately. If the pot de creme gets too hot it will curdle. It takes about 40 minutes to cook, and cream should be smooth. Remove the ramekins from bain-marie, take off the lids and refrigerate until completely chilled.