For the dough, heap the flour on the work surface and press a hollow in the center. Add the egg, water and salt to the resulting “pit” and knead everything into a smooth dough. Place the dough ball in a bowl, brush with oil and let rest covered for an hour.
For the filling, mix all the ingredients until creamy.
Roll out the dough thinly on floured work surface, brush with melted butter and sprinkle evenly with breadcrumbs. Spread the filling on top. Roll up the dough and cut into even pieces. Press the edges of each piece together with fork tines. Wrap the pieces in a cloth and boil in lightly salted water for about 15 minutes.
In the meantime, melt the butter for the butter crumbs. Add bread crumbs and toast. Remove the pan from the heat and mix the powdered sugar evenly into the crumbs.
Remove the finished Štruklji from the cloth and place them on plates. Cover with the crumb mixture, sprinkle with powdered sugar and serve fresh.