Dissolve the yeast and sugar in the milk.  Leave to sit for 5 minutes until frothy.
Place the flour and salt in a bowl, mix in the yeast mixture, butter and yoghurt.
Turn the dough out of the bowl and knead until smooth and elastic.
Place in a lightly oiled bowl, cover and set aside until doubled in bulk – about 1 hour.
Divide the dough into 4 balls.  Roll out into discs.
Heat a griddle or barbecue hot plate and cook naan until golden on each side and well cooked.
Brush with butter or garlic butter.