For the crust:
For the filling:
For the Swiss meringue:
For decoration:
Mix the flour, sugar, salt and cold butter, and beat for 1 minute.
Stir the egg (white and yolk) and add to the dough. Beat again for 2 minutes until smooth.
Cover the dough with plastic wrap and refrigerate for 2 hours.
Take out of the fridge and, with some flour and a rolling pin, roll out the dough until it completely covers baking pan.
Butter the whole baking pan before putting in the dough.
Add the dough and cover the entire baking pan. Bake in the oven, preheated to 400°F, for 10 minutes.
FOR THE FILLING:
Heat the milk in the microwave for 2 minutes and put the cornstarch and sugar in a different bowl, then mix well. While mixing, add lemon juice, lemon zest and yolks (do not throw away the whites), and stir well until there are no lumps left. Next, grind the blackberries in a food processor or manually and strain them to remove all sediment, then add to the mixture. Finally, add warm milk, stirring constantly to prevent the yolks from curdling. Once this is done, put the mixture in a pot over medium heat for 8 minutes, stirring constantly.
When the mixture is ready, you will notice it has thickened. Remove from the heat, stirring all the time, and add butter at room temperature. Keep stirring until the butter has dissolved. Once dissolved, the filling will be done. Cover with plastic wrap and set aside until it has cooled off. Once the filling is cold, pour it over the dough and allow to cool for about 1 hour.
For the meringue:
Put the whites in a bain-marie with sugar and stir until the sugar crystals have dissolved completely.
Once dissolved, beat with a hand mixer for 10 minutes at medium speed.
When the meringue is ready, put it in a pastry bag and use it to decorate the pie together with some blackberries and lemon slices if you wish.
