Beat the eggs, flour, sugar, milk and vanilla essence in a bowl until thick and creamy. Heavily grease a 20 cm (8 inch) round tin or ovenproof dish with the butter and arrange the peaches and blueberries inside. Sprinkle over the lemon zest.
Pour the batter over the fruit and bake in a preheated oven, 190°C (375°F), Gas Mark 5, for 35 minutes until the batter is firm.
Dust with icing sugar and serve warm in wedges.