In a food processor, mix 1 cup of the flour, yeast, and frozen butter until the butter is fully integrated into the flour.
Transfer the flour mixture to a mixing bowl.
Add the rest of the flour, salt, and sugar and mix to combine.
Mix the milk with melted butter. The temperature of the mixture should be warm, but not too hot that you can't touch it.
Add the milk, butter, and egg to the flour mixture and either knead using a stand mixer with a dough hook attachment for six minutes or knead by hand until you can form the dough into a smooth ball.
The dough will be VERY soft. It is nothing like bread dough. Don't worry, you haven't done anything wrong and you should not add more flour.
Place the dough in a covered, lightly oiled bowl and let it sit in a warm place until doubled in size. I turn my oven on to 170 F, wait for it to heat up, then turn the heat off and keep the bowl in there.
Filling Instructions
Mix all ingredients until fully combined.
When the bun dough is done rising, lightly flour a work surface, remove the dough from the bowl, and form it into a rectangle on the work surface. It will still be much wetter than you would expect it to be.
Preheat oven to 400 F.
Spread the filling over the rectangle and roll the dough into a log. It won't be super easy to roll, but don't stress. The only reason you are doing this is to evenly distribute the cinnamon filling inside your cupcakes.
Cut the log into 24 pieces. I found that the easiest way to do this was to cut the log in half lengthwise and then cut each half into 12 pieces.
Place each piece inside of a cupcake liner in a cupcake tin.
Bake cupcakes for 13 minutes or until the tops begin to brown.
Glaze Instructions
Mix all ingredients and drizzle or spread over warm cupcakes.