Sift the flour into a bowl with the bicarbonate of soda and salt. Make a well in the middle and put in the butter, yoghurt and egg and blend. Draw in the flour from the sides and mix to a soft dough. Rest for 15 minutes covered, under a well wrung-out cloth. Take a small piece of dough, flatten it out between the palms of the hands, put in a little of the filling and fold over the edges. Seal.