Position a rack in the middle of the oven and heat the oven to 325 degrees F.
Put the chocolate into a medium bowl. Combine the cream and milk in a small saucepan and bring to a boil over medium heat. Pour the hot cream over the chocolate. Let sit for 30 seconds or so to allow the chocolate to melt, then stir together until smooth.
In a small bowl, whisk together the egg yolks, sugar, and vanilla paste. Slowly stream the egg mixture into the chocolate mixture, whisking constantly. Strain the custard through a fine-mesh sieve into a bowl or pitcher, then pour into six 4-ounce ramekins or ceramic cups or bowls.
Arrange the ramekins in a baking dish or pan and carefully add enough hot water to come about two-thirds of the way up the sides of the ramekins. Carefully place the baking dish in the oven and bake for 30 minutes. Remove the baking dish from the oven and let the pots de creme sit in the hot water for 5 minutes. If they still appear very jiggly in the middle, let them sit for another 5 minutes in the hot water. You want the custards to be very firm around the edges and to barely move toward the center when gently shaken.
Remove the ramekins from the hot water and let cool in a cool area of the kitchen before serving, or chill to serve cold.
The pots de creme can be wrapped individually in plastic wrap and stored in the refrigerator for up to 3 days.