Place the raisins into a small bowl, pour over the rum and leave to soak for 1 hour.
Line the tin with baking parchment.
Put the condensed milk, full-fat milk, sugar, butter and vanilla extract into a large, non-stick saucepan and place over a gentle heat.
Stir until the sugar has dissolved, bring to the boil then reduce the heat and simmer gently for 10-15 minutes. Continue to stir until a sugar thermometer measures 116ºC/240ºF.
Remove from the heat, add the soaked raisins and beat with a wooden spoon for about 10 minutes.
Transfer the mixture to the tin, leave until cold then cut into squares.