Place semolina,butter and sugar in a bowl and rub together with your fingertips. Leave to rest for an hour covered with plastic film.
Add the mahlab (if using),yeast,orange-blossom water and milk and mix together to form a dough.
Turn out on to a work surface,then knead.
Return to the bowl,cover and leave to sit for 30 minutes.
Preheat the oven to 220C.
Knead the dough for five minutes to help bind it together.
To make the filling,combine all the ingredients. Spoon one tablespoon of semolina dough into your hand and shape it into a ball.
Make a hole in the centre and fill with one teaspoon of the filling.
Seal firmly and flatten slightly in the palm of your hand. Press the dough firmly into a ma'amoul mould,then tap out.
Continue with the remaining dough and filling.
Place the ma'amoul about 2.5 centimetres apart on ungreased baking trays and bake for 15 minutes or until golden. Transfer to wire racks to cool. Sprinkle the biscuits with icing sugar (if using) and store in an airtight container for up to two weeks.