1. For the roasted white chocolate, spread your white chocolate chips on a silicone baking mat on a baking sheet and place in a preheated oven of 265 degrees. Every five minutes stir the chocolate. It will become caramelized after 30 minutes up to an hour depending on the caramel hue you are looking for. If you are not using right away, store in a container at room temperature.
2. For the mousse, put the gelatin and cold water in a small bowl and let it sit for about 10 minutes or until it swells, or blooms, and absorbs the water. Stir the softened gelatin with a fork to get rid of any lumps.
3. Bring 1/2 cup of the cream to a simmer in a small saucepan and stir in the gelatin and its soaking liquid. Off the heat, stir the mixture until the gelatin completely dissolves.
4. Pour the hot gelatin mixture over the white chocolate in a heatproof bowl and stir until all the chocolate melts. If your white chocolate seizes up a bit, just continue to whisk until it smooths out again.
5. Beat the remaining cream to medium peaks. Pour the chocolate mixture into the bowl of whipped cream and fold until smooth with a rubber spatula. If you're assembling a cake in a cake ring, use the mousse right away while you can still pour it. If you're serving the mousse on its own , ladle or spoon it into bowls or glasses and chill in the refrigerator for at least two hours before serving.