Heat the oven to 190C (170C fan)/375F/gas 5, and line the base of a loose-bottomed 23cm cake tin with baking paper.
For the base, crush the biscuits in a food bag (or use a food processor) until they are mostly fine. Put the crumbs in a large bowl, add the melted butter and sugar, and stir well to coat. Press the biscuit mix into the base of the lined tin, then bake for 10-12 minutes, until the edges look lightly browned. Remove and leave to cool a little.
Turn down the oven to 160C (140C fan)/325F/gas 3.
For the filling, put the egg yolks, passion fruit juice, lime juice and zest, and salt in a bowl and mix to combine. Stir in the condensed milk and mix again until smooth. Pour the filling on to the biscuit base, then bake for 13-16 minutes, until the custard is set with a very slight wobble in the middle. Leave to cool completely, then chill for one to two hours.
To make the topping, lightly whip the cream to soft peaks, then spoon dollops on to the tart. Top with some of the reserved passion fruit seeds, then slice and serve.
