Whisk the eggs with the brown sugar until smooth and light. Separately mix the hulled buckwheat flour with the baking powder and slowly add the rice milk and oil to the mixture alternately.
Slice or chop the apples, skin on if desired, and sprinkle with a couple of tablespoons of brown sugar. Add 50 of hulled buckwheat, previously toasted for two minutes in a nonstick pan without oil.
Add the apples to the mixture and pour into a 24-cm-diameter baking pan, previously oiled.
Bake in a preheated oven at 180 °C for about 40 minutes.