Roasted White Chocolate Panna Cotta

Preheat the oven to 250°F.
Put the chocolate into an 8 × 11-inch glass baking dish and transfer to the oven. Stir every 10 minutes with a rubber spatula until it turns a nutty brown color, about 1 hour. (The chocolate may be lumpy and not completely smooth; that's fine.) Remove the chocolate from the oven and spread it out on a sheet of parchment paper. Cool to room temperature and then transfer to a heatproof bowl.
Pour the milk into a wide saucepan and sprinkle the gelatin evenly over the surface. Let stand for 10 minutes. Heat the milk over medium heat, whisking, until it just begins to boil. Add the salt and whisk until the gelatin is completely dissolved. Pour about a third of the hot milk over the chocolate and stir slowly until the chocolate is completely melted. Add the remaining milk and whisk until completely combined and smooth. Add the cream and whisk until combined; let stand until room temperature.
Divide the mixture among six 6-ounce glass bowls or ramekins set on a small sheet pan. Pop any bubbles that come to the surface with the tip of a knife. Refrigerate the panna cotta until completely set and cold, at least 2 hours and preferably overnight.
To unmold, fill a small bowl with hot water. Dip the bottom of each bowl in the water for 10 seconds. Wipe the surface of the bowl dry before inverting onto a serving plate.