For the tart shells, in a bowl combine the maida, sugar, salt, baking powder and butter and mix using your finger-tips. The mixture should resemble bread crumbs.
Now bring the mixture together to form a dough. Use some chilled water for this. Add water one spoon at a time and use only as much water as needed to bring the dough together.
Wrap the dough in cling wrap and chill for 1 hour.