Mix your yeast with lukewarm milk. If you use dry yeast you need the milk to be 108F, 42C.
Dissolve your yeast into the milk. Add the sugar, cardamom, salt, and 1-2 cups of flour. Make a slurry.
Add in the rest of your flour and start kneading. Once you have some elasticity in the dough, you can add your butter.
Microwave your butter for some seconds so it softens up to room temperature.
Knead the dough for 7-15 minutes. Knead until the dough is firm enough so it does not break when you stretch a small piece between your fingers.
Cover your bowl with a cloth and let the dough rest in a warm place for 20 minutes.
Bake the dough to 15 round buns by kneading them against the surface in your palm. (If you want even sized buns, measure out the balls with a kitchen scale to be 100-120 grams a piece)
Let your buns rise to double the size. It is good to keep your buns covered with plastic wrap or cloth so the surface does not dry up.
Brush the buns with beaten egg.
Bake at 400F (200C) F for about 14 minutes. The buns should be golden brown on top.
Let the buns cool down. In the meantime make your filling and whip the cream.