Preheat oven to 350°F. Place 6 (½ cup capacity) ramekins in a baking pan and set aside.
Place the egg yolks, rum or brandy, sugar and vanilla in a small bowl and whisk to combine. Cover and set aside until needed.
Pour cream into a small pot and bring to just below a simmer. Whisk in chocolate and stir until it is melted and very well incorporated into the cream. Remove from the heat.
While whisking the egg yolk mixture, very slowly pour in 1/3 cup of the cream/chocolate mixture until well combined. Next, slowly mix this mixture into the pot with the chocolate/cream mixture. Use a small ladle to divide and pour the mixture into the ramekins. Carefully pour hot water into the pan until it reaches halfway up the sides of the ramekins. Bake 30 minutes, or until top is set.
Set the baking pan on a cooling rack. When pots de crème have cooled to room temperature, remove from pan, set on a baking sheet, tent with plastic, and refrigerate 4 hours, until completely set. (Can be made the day before needed.) When ready to serve, set on dessert plates. Garnish each, if desired, with a small dollop of whipped cream and mint spring, and enjoy.
Note: Callebaut Belgian chocolate is sold in blocks in our bakery department.