Using a food processor, blend the strawberries and water until smooth. If you want a chunky sauce, simply slice the strawberries into smaller pieces and move on to step 2.

In a saucepan over medium heat, add the strawberry puree (or pieces), sugar and cornflour, and stir constantly until the mixture thickens and comes to a boil.

Allow to boil for 1 minute, stirring constantly, then remove from the heat. Transfer to a small bowl and allow to cool completely.

Preheat the oven to 180C/350F/Gas 4. Grease a 10x15-inch cake roll pan, and line the base with parchment paper.

Using a handheld or stand mixer, beat the egg yolks on high speed until thick and frothy. Gradually beat in the sugar, vanilla, and yogurt. Add the flour and baking powder, and mix well.

In a separate bowl, beat the egg whites and salt until stiff peaks form. Gently fold into the batter.

Pour the batter into the prepared pan, and spread out evenly. Bake for 8 - 10 minutes or until the cake pulls away from the sides, and a toothpick inserted in the centre comes out clean. Allow to cool in the pan for 5 minutes.

Invert the cake onto a tea towel dusted with a generous amount of icing/powdered sugar.

Gently peel off the parchment paper, dust the cake with more icing sugar, then roll up the cake with the tea towel, starting at a short end. Allow to cool completely on a wire rack.

Using a handheld or stand mixer, whip the heavy cream until it starts to thicken. Add the icing sugar and vanilla and whip to stiff peaks.

Unroll the cake, and spread the strawberry sauce evenly over the cake. Repeat with the whipped cream. (Dollop the cream on top and very gently spread over the jam, trying not to mix the two together.)

Re-roll without the tea towel. Cover and chill for at least 1 hour. Dust with icing/powdered sugar, or garnish with strawberries, then slice and serve.