For the dough, 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 leave in a warm place for 10–15 minutes. Form the dough into five balls.
Preheat the combi oven to 230°C and place an cast iron GN tray to heat.
Roll the dough balls out quite thinly, ideally in a teardrop shape, but really this is just aesthetic. Place the naans onto the hot cast iron GN trays and grill for 2–3 minutes, or until lightly browned. Brush with butter and serve hot.