Add ingredients for blueberry sauce to a medium sauce pan. Place over medium high heat and bring to boil. Reduce to a simmer and cook until berries burst and sauce thickens. Distribute evenly among 4 6-ounce ramekins. Place into a square baking dish. set aside.
Preheat oven to 350 degrees. Place egg yolks in a medium bowl and whisk until blended. Combine cream, milk, sugar, and salt in a medium sauce pan and heat on medium. Stir to dissolve the sugar and heat-through the mixture. Do not let it boil! Remove mixture when sugar is dissolved.
Add vanilla extract to milk mixture. Slowly whisk in 1/4 cup of hot milk mixture into egg yolks to heat them up without scrambling. Whisk in the remaining milk mixture. If you have any egg chunks, strain the mixture.
Ladle the custard mixture into the ramekins very gently so the blueberry sauce does not completely mix with the blueberry sauce. It will swirl a little but not turn completely blue. Fill the ramekins almost to the very top, leaving about 1/2 inch.
Boil water and pour into baking dish, creating a bath for the ramekins. Fill about halfway up the ramekins. Bake in preheated oven for 1 hour 10 minutes to 1 hour 30 minutes, until set but center still jiggles. Cook time depends on the height of your ramekins. Mine were tall so they took about 1 hour 20 minutes.
Remove from oven and carefully remove ramekins from hot water bath. I used a fork and a pot holder to achieve this. Let cool to room temperature and then place in refrigerator to thicken and chill, at least 4 hours.
Once cooled and right before serving, place about 1 - 1 1/2 teaspoons of superfine sugar on top of each custard shake around to create an even layer of sugar. Torch with blow torch to caramelize the sugar. Serve immediately.