Preheat the oven to 180 degrees. In a bowl sift the rice flour and plain flour, powdered sugar and salt. Add the butter pieces previously softened and knead the mixture until it is grainy. Add the dark chocolate chips and knead well to distribute them well. Wrap the dough in plastic wrap and let stand for about half an hour in the fridge. After the 30 minutes, form many balls from the dough, taking care not to work too much otherwise the butter warms up again. Crush each ball, lay on the plate of the oven where the wax paper will be laid. Brush with milk and drop the cornflakes. Bake the biscuits for 15 minutes until golden brown. Once cooled add a sprinkle of powdered sugar and they are ready to be enjoyed.