Heat the milk, butter and powdered sugar together in a saucepan. Once the butter is melted, remove the pan from heat and cool the mixture until it is lukewarm.
Pour the milk mixture into a large mixing bowl and add the yeast.
Grind the cardamom seeds into powder and add to the mixture. Slowly add the flour until it's not too sticky to knead (you might need a bit less flour than called for).
Knead the dough on a floured surface for about five minutes. Cover and let rise for 30 minutes.
Chop the chocolate into small pieces (unless you're using chocolate chips). Add the chocolate to the dough and mix until incorporated.
Slice the dough into about 20 pieces. Roll each piece into a ball and set seam down on a baking sheet lined with baking paper. Cover and let rise again for 45 minutes.
Preheat oven to 440°F (230°C). Whisk the egg together with a splash of milk and brush onto the top of each bun.
Bake buns for 8-10 minutes, until the tops are golden brown.