Cut all the fruits (except the reserved strawberries) into slices and drizzle with the lemon juice. Divide equally among four individual, heatproof gratin dishes.
Put the egg yolks in a large heatproof bowl, add the sugar and whisk using an electric hand mixer until the mixture is pale and creamy.
Place the bowl over a saucepan of simmering water and continue whisking until the mixture thickens, adding the wine or sherry a little at a time, followed by the cream. (It is important that the water in the pan does not boil; if it is too hot, the egg yolks will cook too quickly.)
Preheat a grill to its hottest setting. Pour the thick, mousse-like mixture over the fruits and place the dishes under the grill. Cook for a few minutes until lightly browned on top, then serve immediately, decorated with a whole strawberry and a sprig of mint on each dish.