Sift flour on a horizontal surface. Make a well and place butter, sweetener and salt in the center. Combine with a pastry blender until mixture resembles oatmeal. Add yolks and knead just until a soft dough is formed. Wrap and refrigerate for an hour.
Roll out dough and line bottom and sides of a tart pan. Prick bottom with a fork.
Cover crust with apples. Sprinkle sweetener and cinnamon. Bake in oven 350 °F (180 °C) during 20 minutes. Remove from oven.
Combine milk with yogurt, sweetener and beaten eggs. Cover apples with this mixture and return to oven for 15 minutes more. Remove and cool on rack.
Melt butter, add flour, sweetener and cinnamon. Mix. Spread streusel over the apples and broil in oven until golden.