For the dough:

1. Heat the milk in a small pot until slightly warm (about 110 degrees).
2. Add the milk and the yeast to a bowl attached to a stand mixer with the dough hook attachment. Let the yeast dissolve and activate for about 5 minutes.
3. Add the egg and mix until just combined.
4. Next mix in the flour, sugar, vanilla, cardamom, and salt. Mix until combined. Finally, mix in the butter about a tablespoon at a time. Continue to knead until the dough is thoroughly mixed.
5. Transfer the dough to an oiled bowl and let rise until it has doubled in size—about 1 hour.

For the filling:

1. In a medium bowl, beat the butter, sugar, cardamom, vanilla, and bourbon until its light and fluffy.

For the assembly:

1. Roll the dough out into a rectangle that about 1/4 inch thick.
2. Spread the filling evenly over the dough.
3. Next, fold one of the dough 1/3 of the way over its self and then do the same with the other side so that the filling is totally covered, like folding a piece of paper into thirds. Use your rolling pin and flatten out the dough just a little.
4. Cut the dough into 2cm strips. Wrap each piece around two of your fingers once to create a roll then loop the remaining length around the top, tucking the end underneath.
5. Line two baking sheets with parchment and place the rolls on top, while leaving space for them to rise. Let them rise again for 30 minutes and preheat the oven to 350 degrees.
6. Lightly beat the egg and brush over all the buns right before baking. 
7. Bake for 25 minutes.

For the glaze:

1. Combine the powdered sugar and bourbon in a bowl until there are no lumps left.