Ingredients

• butter (melted, for greasing)
• 4 eggs
• 125 g (41/2 oz) caster sugar (plus 3 tbsp for sprinkling)
• 2 tblsp warm water
• 1 tsp vanilla extract
• 125 g (41/2 oz) plain flour (plus extra for dusting)
• for the filling
• 200 g (7oz) rhubarb (about 2 stalks, trimmed), cut into 5mm (1/4 in) slices
• 125 g (41/2 oz) caster sugar
• 200 ml (7fl oz) milk
• 1 vanilla pod, split lengthways, or 2 tsp vanilla extract
• 3 egg yolks
• 15 g (1/2 oz) cornflour
• 100 ml (31/2 fl oz) whipped double or regular cream (measured when whipped)

Method

1. Preheat the oven to 190°C (375°F/Gas 5). Line the base of the Swiss roll tin (25 x 38cm/ 10 x 15′) with baking parchment, brush the base and sides of the tin with melted butter and dust with flour.
2. Using a hand-held electric beater or an electric food mixer, whisk together the eggs, caster sugar, water and vanilla extract until light and fluffy.
3. Sift in the flour, about one-third at a time, and fold it into the mixture. Carefully pour the mixture into the prepared Swiss roll tin and bake in the oven for 12–15 minutes or until the centre of the sponge is slightly springy to the touch and the edges have shrunk a little from the sides of the tin.
4. Take a piece of baking parchment slightly larger in size than the tin and spread out on a work surface.
5. Sprinkle the paper evenly with caster sugar (this is to stop the cake sticking to the paper). Quickly flip the Swiss roll tin over onto the sugared paper, then carefully remove the tin and baking parchment from the bottom of the cake.
6. Place a clean, slightly damp tea towel over the cake while it cools – this will prevent it drying out and cracking when you roll it.
7. Meanwhile, make the filling. Place the rhubarb in a saucepan with 75g (3oz) of the caster sugar and 25ml (1fl oz) of water and place on a medium heat, stirring to dissolve the sugar. Bring to the boil and allow to boil, uncovered and stirring regularly, for 10–15 minutes or until the rhubarb is completely soft and the mixture is quite thick.
8. Tip out onto a plate and allow to cool.
9. Next make the custard. Place the milk and the split vanilla pod (if using) in another pan and bring to the boil.
10. Whisk the egg yolks (and vanilla extract, if using) with the remaining sugar (I like to use a hand-held electric beater for this) for a few minutes or until pale and light. Then briefly whisk in the cornflour.
11. Pour the hot milk and vanilla pod (if using) onto the egg mixture, whisking as you pour, then tip it all back into the saucepan and cook, stirring all the time, over a low heat for a few minutes or until it forms a thick custard.
12. Pour it into a bowl and allow to cool, then fold in the cooled rhubarb and the whipped cream – you can leave it slightly marbled (not fully mixed) if you prefer.
13. When the sponge is completely cold, spread over the rhubarb and custard mixture, then, with one of the short sides facing you, roll up the Swiss roll away from you and carefully transfer to a serving plate.
14. Sprinkle with a little extra caster sugar to finish, then cut into slices about 2cm (3/4in) thick to serve.