3/8 cup superfine sugar
7/8 cup All purpose flour
1/4 cup fresh or frozen blueberries
Strained juice of 1 small lemon
1 level teaspoon arrowroot
1 tablespoon water
1/2 cup Greek yoghurt
1 level tablespoon pistachio nuts, skinned and chopped
OVEN: Preheat to 200°C (400°F)
1. Grease a swiss-roll tin 13 x 9 inch and line it with nonstick baking paper.
2. Whisk the eggs and 1/4 cup of the sugar with an electric or hand whisk until the mixture is pale, very fluffy and so thick that a ribbon of mixture trailed onto it from the whisk stays on the surface.
3. Sift the flour over the mixture and gently fold it in, using a metal tablespoon. Pour the mixture into the tin and gently spread it out with a palette knife. Bake for about 10 minutes, until well risen, firm to the touch and golden.
4. Meanwhile, place a sheet of nonstick baking paper on a damp teacloth and sprinkle with 1 teaspoon of the remaining sugar.
5. Quickly turn the sponge onto the paper, with a short side towards you, and peel off the cooking paper. Trim off the crisp edges with a sharp knife. Carefully roll the sponge away from you, rolling sponge and paper together. Place seam side down on a wire rack to cool.
6. Gently heat the blueberries with the remaining sugar and the lemon juice in a small, covered saucepan until the juices begin to run. Remove from the heat. Blend the arrowroot with the water, then stir into the fruit. Return to the heat and continue cooking, stirring gently, until the liquid thickens and clears. Pour into a wide bowl to cool.
7. When both roll and blueberry filling are cold, carefully unroll the sponge. Spread the yoghurt over it, then cover with the blueberry mixture, leaving a narrow border all round. Roll up from the other short edge. Scatter the nuts in a line along the top. Lift the Jelly roll onto a serving dish, cover with an upturned plastic box and put in a cool place until serving time.
If this is more than an hour away, put the roll, covered, in the refrigerator, taking it out 30 minutes before serving.
You can use blackcurrants or bilberries instead of blueberries, but they will need a little more sugar. You can also fill the roll with raspberries, which need no sugar or cooking.