For the dough, combine and mix flour, sugar, diced butter and sour cream. Stir well until dough comes together. Roll out the dough, shape into a flat disk to fit a 9 inch pie plate. Transfer dough to pie plate and trim edges of dough leaving some overhang. Flute the edges. Use a fork to prick the bottom of the dough. Refrigerate for 10 minutes.
After 10 minutes, cover the dough with parchment paper and fill it with pie weights or dried beans. Bake for 25 minutes, remove weights and bake again for 5 minutes.
In the meantime, beat the egg, add the mascarpone and stir well to combine. Add 2/3 of the sugar and 1 tbsp of almond powder.
Peel the apples, cut in four and remove the core. Cut apples into slices. Put in a bowl and cover with lemon juice and 1tbsp of sugar.
Cover the bottom of the dough with the rest of the almond powder. Pour in the Mascarpone cream and spread well with the back of a spoon. Arrange the apple slices on top, sprinkle with almond slices and some sugar.