Mix butter, sugar, salt and cardamom in a large bowl.
In another container mix milk and yeast and let it stand for about 5 minutes until foamy.
Add milk mixture to the butter mixture and mix well.
Add flour and knead until well incorporated and dough is elastic.
Cover the bowl and let it rest until dough has doubled in size.
Filling
Mix the filling ingredients and set aside.
Making the buns
When dough has risen, place it in a floured surface, cut in half and return one half to the bowl.
With a rolling pin, open half the dough to a rectangle of about 15inx20in (40cmx50cm) and spread half the filling over it.
Fold it like an envelope (fold the lower third to the top and the upper third over the folded lower third) creating three layers.
Now, again with the rolling pin, open the dough until it is about twice the folded size (still maintaining the rectagle shape).
From the longest side, cut 2 inch strips and then cut each strip in half up to about one inch from the edge (the top of each strip must remain together - like a pair of pants).
Wrap each "pair of pants" around your fingers finishing with some dough on top, like a knot and place each roll in a baking sheet layered with parchment paper (or a silicon mat).
Repeat the process with the other half of the dough.
Let the rolls rest for about 30 minutes.
Preheat the oven to 350F/180C.
Brush each roll with the beaten egg and dust with caster sugar.