Mix egg, wholemeal flour, skimmed milk and mineral water to a smooth dough. Peel the grapefruit and orange so that the white skin is completely removed. Remove the fillets with a sharp knife between the parting skins.
Brush a small pan with oil, add the dough and bake from both sides. Take out the pancakes, fill them with half of the grapefruit and orange fillets (use the rest for other purposes) and arrange them on a plate.
Drizzle the pancakes with honey and decorate with mint before serving.