Preheat the oven to 180 °C. Line a baking tray with baking paper.
For the curd filling, cream butter until fluffy. Stir in sugar, yolks and lemon zest, then mix in curd and cornstarch.
Cut the puff pastry into 8 squares. Place 1-2 tsp curd filling in the center of each square. Fold the 4 corners over the filling and press together in the center. Brush the golaches with beaten egg and bake in a hot oven for about 20 minutes.
Let cool before serving and sprinkle with powdered sugar.