500g small strawberries, hulled, or halve large ones
To make the pastry, rub the flour and butter together (or whizz in a food processor), then mix in the sugar. Add the egg yolks and mix until you have a dough - you might need to add a splash of cold water if the mix is dry. Knead briefly until smooth, then wrap and chill for 15 minutes.
Heat the oven to 190C/fan 170C/gas 5. Lightly butter a 24cm tart tin. Roll out the pastry (use a bit of flour to stop it sticking) and use to line the tart tin, then chill again for 25 minutes. Line the base of the pastry with baking paper and beans and bake for 15 minutes. Reduce the heat to 150C/fan 130C/gas 2 and bake for a further 10 minutes, then remove the baking paper and beans and cook for 10 minutes more.
Leave the pastry to cool a little, then remove from the tin and transfer to a serving plate. When it’s totally cold, spread the mascarpone or clotted cream over the flan base. Melt the jelly crystals in 175ml hot water, cool and, when it starts to thicken, add the strawberries and carefully mix to coat them. Put the jelly-coated strawberries upright in a single layer in the case and spoon in enough jelly to cover and leave to set.