For syrup, mix sugar with 120 ml of water, lemon and orange juice and zest. Bring to a boil, cook for 5 minutes. Cool, refrigerate for 1 hour.
Meanwhile, for the pie, separate the egg whites from the yolks. Beat the yolks with sugar into a fluffy light foam. Whisk egg whites separately. Add flour to the yolks, then yogurt, zest and lemon juice, mix until smooth, gently combine with proteins.
Transfer the dough to a greased form and bake in an oven preheated to 180 ° C for 50-60 minutes. The top of the finished cake should be brown. Serve hot or cold with syrup.