Preheat oven to 210C. Combine yeast with 50ml lukewarm water and stand until foamy. Place flour in the bowl of an electric mixer fitted with a dough hook. Make a well in the centre, add eggs, sugar, lemon rind and a pinch of salt to well. Add butter a little at a time, mixing until combined, then add yeast mixture and mix until a ball forms (10-15 minutes). Dough shouldn't be sticky, so add a little more flour if necessary, then stand, covered, in a warm place until doubled in size (1 hour).
Roll dough on a lightly floured surface to a 28cm-diameter circle and place on a baking-paper-lined oven tray. Fold over edges, pleating as you go, to form a 2cm border.
For sugar topping, scatter butter slices in an even layer within pastry border, scatter over sugar in an even layer, bake until puffed and golden (15-20 minutes). Serve warm or at room temperature, dusted with icing sugar, scattered with blueberries.