In a large mixing bowl, combine water, melted butter and sugar. Sprinkle the yeast over the mixture and let stand for about 5 minutes or so, until foamy.
Add the eggs, milk powder and salt and use a wooden spoon to stir everything together. Add 5 cups of flour, one cup at a time, stirring often until a soft dough is formed. Turn it over into a floured surface and knead for about ten minutes, until the dough is smooth and elastic. Use just enough flour from the remaining 1 cup during kneading until the dough is no longer sticky.
Shape kneaded dough into a ball and place in a bowl. Cover with plastic wrap and let rise for about an hour, until doubled in size.
Meanwhile, make the filling. Stir together softened butter, sugar, cinnamon, and cardamom until combined. Set aside.
Punch down risen dough and roll into a 15x21 rectangle. Spread the filling on the surface. Use a spatula, brush or back of the spoon to press the filling into the dough. Starting on the short side of the dough, fold 1/3 of it into the center, then fold the other third over to center too, covering the first flap. This can also be called as the business letter fold. Briefly roll the pin over the folded dough just to stretch the width out to 10-12 inches.
Using a knife or pizza cutter, cut strips of dough starting from one long side to the other. The strips should be about 2 cm in thickness. You will be able to make 15-22 strips. To assemble the rolls, take one strip, hold one end with your thumb and next three fingers. Wrap the strip around your fingers two times, covering the thumb as well, then pull the dough under and slip it through the opening where your thumb is. Pull it upwards and let it cross over the bun and tuck it in the other side. Watch the short video for assistance.
Place each roll on a baking sheet that is lined with parchment paper. Cover it loosely with a plastic wrap and let rise for about an hour, until double in size.
Preheat oven to 350 F. Beat 1 egg with 1 tablespoon milk and brush this glaze on the surface of the risen rolls. Sprinkle a little sugar over top of the rolls and bake for about 22-25 minutes, until lightly golden.