Mix the flour, sugar and lemon zest together. Add the cold butter in small pieces and knead with your hands or a hand mixer until the dough has a crumbly consistency. Add the egg and knead into a smooth dough. Shape the dough into a ball, wrap it in cling film and place in the refrigerator for 30 minutes.
Grease the wells of a muffin tin with oil or butter. Place a thin strip of parchment paper in each well, sticking out of the well at both ends. This strip can later be used as a lifting aid to help loosen the tartlets from the tray. Preheat the oven to 200 ° C.
Roll out the dough about 3 millimeters thick. Using a cup, cut out round circles that are slightly larger in diameter than the muffin cups. Pour the batter into muffin wells. Pour approx. 1 1/2 tablespoon pudding into each well and sprinkle 2 tablespoon frozen berries on top. If you like, you can mix some coconut flakes with sugar and pour over the berries.
Bake the tartlets for 20-25 minutes. Let cool, remove from the tray and serve.