Line the base and sides of a 30 x 23 cm (12 x 9 inch) Swiss roll tin with a single sheet of nonstick baking paper, cutting the paper in the corners. Put the eggs, sugar and lemon rind in a mixing bowl set over a saucepan of simmering water. With an electric whisk, beat the mixture for 10 minutes until it is thick and the mixture leaves a trail over the surface when the beaters are raised.
Remove the bowl from the saucepan, sift the flour over the surface and gently fold in. Pour the mixture into the tin. Bake in a preheated oven, 200°C (400°F), Gas Mark 6, for 8–1 0 minutes until the top springs back when pressed with a fingertip.
Put a piece of nonstick baking paper (about the same size as the tin) on the work surface with a narrow edge towards you and sprinkle with sugar. Quickly turn the sponge out on to the paper, peel off the lining paper and cover with a second piece of paper. Loosely roll up the sponge, starting from the edge nearest you. Leave loosely wrapped in the sugared paper to cool.
Unroll the sponge and remove the centre paper. Mix the fromage frais and quark with the sugar and spread over the cake. Sprinkle with the fruit, reserving a few for decoration, then re-roll the sponge, using the sugared paper underneath to help you (but being careful not to roll the paper up inside the roulade) and transfer to a serving plate. Decorate with the remaining fruit and serve cut into thick slices.