1 tsp each cornflour, white vinegar and vanilla extract
4 large egg whites
100g caster sugar
100g icing sugar, plus a little extra
150ml tub lactose free or rice double cream
Pour lactose free milk into a pan. Split vanilla pod lengthways and scrape out seeds, adding both to the pan. Slowly bring to the boil. Reduce heat and simmer for 2 mins.
Meanwhile, put egg yolks, sugar and custard powder/cornflour into a bowl. Using an electric beater, whisk until pale and fluffy. Whisk in a third of the hot milk, then add remainder. Add mixture to the pan and bring to the boil, stirring, until the custard is thickened.
Reduce heat and simmer for 2 mins, stirring constantly. Fish out vanilla pod and pour into a bowl. Cover surface with cling film, leave to cool, then chill. Can be made 1 day ahead. Heat oven to 160C/140C fan/gas 3. Line the base and sides of a 23 x 33cm Swiss roll tin with baking parchment.
Blend cornflour, vinegar and vanilla extract to a smooth paste. Tip egg whites into a clean bowl. Mix together sugars in a separate bowl. Whisk egg whites until stiff, then gradually whisk in the sugar, alternating with a little paste until the mixture is thick and glossy.
Spoon into the prepared tin and smooth the top. Bake for 20 mins until crisp on top. Meanwhile, whisk the lactose free cream and fold into the custard. Remove the meringue from the oven and turn out onto a sheet of baking parchment, peel off the lining paper and leave to cool for a few mins.
Spread the custard evenly over the meringue to within 5cm of the short ends and to the edge of the long ends. Scatter with the raspberries. Using the parchment to help you, roll up the meringue from one short end. Transfer to a flat plate and dust with icing sugar.