Measure the butter for the filling, put it on a small plate or bowl and leave it to soften in room temperature.
Warm the milk in a pot up to 37 degrees C if using fresh yeast and 42 degrees C if using dried.
Pour the milk into a large bowl and mix the yeast in until dissolved. Hand whisk works well here unless you are using a kitchen aid.
In the same pot melt the butter and let it cool.
Add sugar, salt and cardamom into the milk-yeast mixture and mix until salt and sugar have dissolved.
Start adding the flour. You can easily add at least the half of the flour while you are still using the hand whisk. Once the dough starts thickening you can use a wooden spatula or something similar before getting your hands in.
Keep adding the flour gradually and start kneading it with your hand. Add the melted butter (must not be hot, it will kill the yeast) towards the end and keep kneading until the butter has mixed in and the dough no longer sticks to the bowl. You can add some more flour if the dough is very sticky.
NOTE: The softer you are able to leave the dough the softer your buns will be. So, here lies the tricky part. Too much flour makes the dough and buns dry and too little flour makes it difficult to work with it. So, the dough should definitely be workable, in other words not stick to your hands too much but then at the same time not too hard. I am sure you will get what I mean and you can work out the right consistency once you have your hands in it!
Once you have your 'dough ball' ready, sprinkle little flour on top of it and cover the bowl with a cloth. Let the dough rise, covered with a cloth, in a warm draft-free place until it doubles in size (30-60 minutes).