In a bowl, beat the eggs, sugar and grated lemon peel by hand or, more conveniently, with an electric whisk. Add the mascarpone and the sifted flour, a little at a time, stirring constantly. Then add the baking powder and stir again. Wash and peel 1 peach (or 2 if they’re small), chop it into small pieces and add them to the bowl; stir thoroughly until the mixture is homogeneous, then pour it into the cake tin, greased with butter and dusted with flour. Carefully wash the other peaches, cut them into thin slices – leaving the skin on – and arrange them on the surface like the petals of a flower; form 3 concentric circles, placing the slices with the part with the skin on facing outwards. Bake the cake in a preheated oven, at 180 °C, for 45 minutes (check to make sure it doesn’t brown too much on top and, if necessary, cover with kitchen foil). When the time is up, use a toothpick to see if it’s cooked: stick it into the centre, and if it comes out dry the cake is ready. When it has cooled down, remove the cake from the tin and sprinkle it with icing sugar.