Preheat the oven to 170°C (338°F). Grease the bottom and sides of the springform pan well with butter, then set it aside.
In a bowl, combine the flour, both types of sugar, and baking powder. Then add the cold butter, cut into cubes, and rub it into the flour mixture until you get a crumbly texture, similar to sand. Add the egg and 1–2 tablespoons of ice-cold water. You don’t need to knead the dough for long, just enough to bring everything into a compact ball. If the dough is very soft, put it in the fridge to firm up. If not, continue with the preparation. Roll out the dough on a well-floured piece of baking paper. Transfer the dough to the baking pan. I usually do this using a rolling pin. It may crack here and there; this is expected to happen. Patch it up with your fingers and press it in well. Trim off any excess dough hanging over the edges.
Mix the pudding powder with a few tablespoons of cold milk until smooth and lump-free. Bring the rest of the milk together with the sugar to a boil, then add the pudding mixture. Cook until it thickens.
Immediately after removing the pudding from the heat, vigorously stir in the sour cream (mileram) to prevent lumps from forming. Spread the still-warm cream over the pastry and smooth the surface.
Next, add the fruit on top of the cream. If you’re using frozen berries, there’s no need to defrost them first.
Bake the mileram cake in the preheated oven, on the middle rack, for 70 minutes.
After baking, the center will still be wobbly, like cheesecake. That’s normal! It will firm up as it cools. Let the cake cool to room temperature, then pour red cake glaze over the top.
Refrigerate the cake for several hours, ideally overnight. The next day, carefully remove it from the springform pan and decorate as desired. I used whipped cream, fresh raspberries, and mint leaves.