Dough:
Put butter and milk in a saucepan and heat until the butter is melted and the milk is lukewarm.
Crumble the yeast into a large bowl or dough bowl and add the lukewarm milk/butter mixture.
Stir the mixture with a hand whisk until the yeast is dissolved in the liquid.
Add sugar and salt and stir again until the sugar and salt are dissolved.
Add cardamom and flour, and knead the dough until it is smooth and elastic.
Cover the bowl with a damp cloth or a shower cap and let it rise for 40 minutes.
Filling:
While the dough is rising, mix the filling together.
Put soft butter, sugar, and cinnamon in a bowl.
Mix the ingredients thoroughly—perhaps with an electric mixer—until the filling becomes a smooth and even mass. Set aside.
Take the dough out of the bowl and punch it down.
Roll the dough out into a rectangular sheet as shown in the picture.
Spread the filling on the dough and fold one side in half over the dough.
Repeat with the other side, folding it over the first, so you now have a rectangular dough strip.
Cut the dough into strips approximately 2 centimeters wide.
Twist the dough strips in the following way:
Take one end of the strip between your index finger and thumb.
Twist the strip around your fingers 2-3 times. Finish by taking the other end of the strip between your index finger and thumb and over the twists. Pull your fingers out, so the end of the dough is tucked into the dough.
Place the cinnamon twists with the twists facing up on a baking sheet lined with parchment paper.
Let the cinnamon twists rise again for 40 minutes.
Whisk the egg with a fork in a deep plate.
Brush the twists with the beaten egg and bake them at 225 degrees Celsius (437 degrees Fahrenheit) without convection for 6-8 minutes.
Let the cinnamon twists cool on a wire rack before eating.