Delicately wash the strawberries, without removing the stems, and leave a few aside for decoration. Remove the stems from the others and cut them into small pieces. Put the pieces of strawberry in a bowl with the sugar and the lemon juice. Mix and leave to marinate. In the meanwhile prepare the biscuit-base: beat the egg yolks with the sugar, keeping the whites to one side. Add the juice and grated rind (only the yellow part) of half a lemon, the flour, potato starch and baking powder sifted together, and finally the egg whites beaten to "stiff peaks", a little at a time, stirring from bottom to top. Line a baking tray, measuring approximately 25 x 35 cm (use one that is similar in shape and size, or slightly larger than the container in which you will prepare the dessert), with greaseproof paper and tip the mixture into it. Level it with the back of a spoon and cook it in a preheated oven at 180 °C for roughly 10 minutes, until the surface is golden brown. Take it out of the oven, delicately detach the biscuit-base from the paper and transfer it onto the plate (or into the oven dish, or…) chosen for the “tiramisu” (if the base is too big, cut it down to size). Distribute on top the pieces of strawberry and the juice that has formed while marinating, which will be absorbed by the biscuit (exactly what’s needed!). In a bowl, mix the mascarpone, the yogurt and the sugar together thoroughly using a whisk. Pour the cream on top of the layer of strawberries, level it and decorate with the strawberries that you set aside, whole if they’re small or in pieces, or slices, if they’re large. Leave to rest in the fridge for at least an hour; if any is left over, the day after it will taste even better. In the right season, when the strawberries are ripe (thanks to the sun!), this is a delicious dessert.