Preheat oven to 300 degrees.
Place heavy cream and milk in a small saucepan over medium heat and bring to a simmer.
Add the finely chopped chocolate to the hot cream and stir until all the chocolate is completely melted.
Combine the yolks, sugar, salt and vanilla in a medium bowl and whisk for 2 minutes until the yolks are lightened in color.
Slowly pour the cream and chocolate mixture into the yolks, whisking constantly until combined.
Strain the mixture through a fine mesh sieve to get rid of any egg solids that may have formed.
Divide evenly among 6 heat proof 6 oz (4 oz of liquid in each).
Place the ramekins into a 9 x 13 baking pan and place on an oven rack that is partially pulled out.
Pour very hot water into the baking pan until it comes halfway up the sides of the ramekins, being careful not to overfill or get water into the ramekins.
Bake for about 30-35 minutes until the edges are set and the center is still slightly jiggly.
Carefully remove the ramekins from the water bath and let cool for about 20 minutes.
Cover and refrigerate the pot de cremes for 2 hours prior to serving.