Sift the flour, sugar, salt, and baking powder into a bowl. In another bowl, mix together the milk and oil. Make a well in the centre of the flour mixture and pour in the liquid mixture. Slowly mix together the dough by working from the centre and incorporating the flour from the edges of the 'well' to make a smooth soft dough. Knead well for 8-10 minutes, adding a little flour if the dough is too sticky.
Place the dough into an oiled bowl, cover with a damp tea towel and leav in a warm place for 10-15 minutes. Form the dough into 5 balls.
Preheat the grill to medium and place a heavy baking sheet on the upper shelf of the grill to heat.
Roll the dough balls out thinly and sprinkle over with fresh garlic and coriander. Press the toppings in slightly.
Place the naans on the hot baking sheet and grill for 1-2 minutes or until lightly browned. Brush with butter if desired. Serve hot.