Sift together the flour, sugar, salt and baking powder in a bowl. Mix the milk and oil together in a separate bowl. Make a well in the centre of the dry ingredients and pour in the liquid ingredients.
Slowly mix together the dough by working from the centre and incorporating the flour from the edges of the well until you have a smooth, soft dough. Knead for 8-10 minutes, adding a little flour if the dough is too sticky.
Place in an oiled bowl, cover with a damp tea-towel and leave in a warm place for at least an hour, until the dough has doubled in size. Then knock back and form into five equal-sized balls.
For the filling, pulse together the pistachios, raisins and sugar in a food processor until the mixture forms a coarse powder. Divide into five equal portions.
Preheat the grill to its highest setting and place a heavy baking sheet on the top shelf to heat.
Roll out each of the five portions of dough balls into thick circles. Fill half of each circle with one portion of the filling leaving about a one-inch margin around the edge. Wet the dough around the edges with a little water and fold each circle in half to enclose the filling. Pinch the dough around the edges to close.
Gently roll out each naan into a teardrop or oval shape. Sprinkle over the flaked almonds. Place the naan on the hot baking sheet and grill for about 1-2 minutes until there are nice brown spots on the surface. Brush with the melted butter and serve hot.