For the sauce; pour the sugar into a clean, dry saucepan. Melt over medium heat, stirring until the sugar melts and turns deep golden. Turn the heat off. Carefully pour in the cream (sugar will spit a little and turn to toffee).
Return pan to medium-high heat, cook whisking until the toffee dissolves and sauce is smooth. Simmer gently 1 minute to thicken slightly. Whisk in the salt. Set aside to cool 15 minutes.
Combine mascarpone, cream and vanilla. Spoon onto large serving platter. Scatter over the raspberries. Drizzle with caramel sauce. Serve.