Preheat the oven to 170°C (340°F). Grease a 24 cm (9-inch) round baking pan.
In a bowl, mix the flour, butter, powdered sugar, and egg yolks until a smooth dough forms. Shape into a disk and press it evenly into the base of the pan. Chill while preparing the filling.
In a large bowl, combine the egg yolks, sour cream, flour, and semolina. Mix until smooth, then add the vanilla seeds and lemon zest.
In a separate bowl, beat the egg whites with a pinch of salt until soft peaks form. Gradually add the sugar and continue beating until stiff peaks form.
Gently fold the whipped egg whites into the sour cream mixture, using light, upward movements to keep the mixture airy.
Pour the filling over the prepared crust and smooth the top.
Bake for 40–50 minutes, until lightly golden and set. Turn off the oven and leave the cake inside with the door slightly open for about 1–2 hours to cool gradually.
Refrigerate for a few hours before serving. Dust with powdered sugar if desired.