Slice the peeled oranges into 5mm slices. Lay them out in a dish.
Squeeze over the juice of the lemon and sprinkle with the sugar. Cover the dish and place it in the fridge to sit while the rest of the tart is made.
Pastry
Using a food processor or a pastry cutter, cut the cold butter into the flour until it resembles coarse breadcrumbs. Stir in the sugar and salt.
Tip in the lightly beaten egg and just enough milk so the mixture forms a stiff dough ball. Don't over knead it, it should just come together.
Place the dough in a clean bowl and cover the bowl with a plate. Put the bowl in the fridge and let the dough chill for at least 30 minutes.
Preheat the oven to 180°C (356°C), fan-bake.
Grease a 23cm tart tin and lightly flour a bench.
Place the dough on the floured bench and roll it out until it's about 5mm thick. Line the tart tin with the dough and trim off any excess. Prick the bottom of the pastry with a fork a few times, then place the pastry back in the fridge for 10 minutes to chill again.
Take the tart tin from the fridge and cover it with a sheet of baking paper and fill the tin with baking weights (or rice).
Bake the covered pastry for 10 minutes, then remove the baking paper and weights and continue baking the pastry for a further 10-15 minutes until golden brown and cooked through. Leave the pastry to cool.
Lemon Mousse
In a mixing bowl, beat the cream with the cornstarch and sugar until it holds firm peaks.
Fold in the yogurt and lemon curd carefully.
Tip the lemon mousse mixtue into the cooled tart case and place in the fridge for 2 hours to chill.
Serving
Once the tart has chilled, arrange the macerated oranges over top (leaving the juice behind). Sprinkle with freshly shredded mint leaves.