In a small bowl, sprinkle the gelatin over the milk. In a medium size pot over medium/low heat, bring the sugar, vanilla beans, salt and 2 cups of the heavy cream to a boil, whisking occasionally. Remove from the heat. Take out the vanilla beans and scrape out their seeds, returning them to the pot. Discard the pod.
Stir the gelatin mixture and add to the pot, stirring to dissolve. Pour the panna cotta into a large metal bowl and cool, stirring occasionally. Cool over cold, but not iced, water to speed the process.
Whisk the remaining cup of cream to soft peaks. Stir the sour cream to an even consistency before folding it into the whipped cream, then fold this into the cooled mixture. Fold gently, but thoroughly, to keep the mixture light and airy.
Pour into a jelly mold or into individual ramekins and refrigerate. Can be made the day before serving.
To serve the panna cotta, unmold by dipping into some hot water and then inverting onto a serving platter, or individual dessert plates in the case of ramekins. You may have to run a knife around the sides of the ramekins and release the panna cotta on an angle over the plates. Pour a little of the chocolate Brandenburg No.3 sauce over the top (or around) and decorate with the praline.
Prepare a tray lined with parchment paper.
Caramelize the sugar, syrup and water over medium high heat until medium dark. The trick is to get it dark, but not burnt. Keep a close eye (and nose!) on it and be quick to take it off the heat as soon as it has darkened, add the hazelnuts and soda, mix quickly and spread immediately out on the tray. Cool, then break into chunks.
* To peel hazelnuts perfectly before roasting, combine a tablespoon of baking soda with 1 quart of water water in a saucepan and bring to a rolling boil. Blanch the hazelnuts for about 3 minutes minutes and drain in a colander. Run cold water over the nuts and peel. The skins will slide off easily with your fingers. Toast the hazelnuts to a light brown color in a dry frying pan over medium heat or in the oven.
Chocolate Brandenburg No.3 Sauce
You can make your own caramel and blend with fine chocolate into the heated wine, but for a cheeky short cut to a fun sauce, you can bring ¼ cup Venturi-Schulze Brandenburg No.3 wine to a rolling boil, lower the heat and add the Caramilk bar, broken into squares. Stir and when it is completely melted, strain and serve warm.