Place the sugar and rose petals in a food processor and pulse to make a puree. Pour the double cream and milk into a saucepan and add the sugar and rose petal puree. Bring to a simmer over a medium heat, stirring until the sugar is dissolved. Remove from the heat.
Whisk the egg yolks and slowly add to the hot cream mixture, whisking all the time. Return the mixture to a medium heat and cook, stirring constantly, until it is thick enough to coat the back of a wooden spoon. Pass the mixture through a fine sieve into a bowl and allow to cool.
Using an ice-cream machine, churn the ice-cream as per your machine's instructions.
If you haven't got an ice-cream machine, put the mixture in a plastic container, cover and place in the freezer. You'll need to stir the ice-cream every half hour for at least two hours.