Add the egg whites to the butter, then add the yeast mixture, cream, vanilla extract, lemon zest, cinnamon, salt, and flour. Beat with a dough hook until the dough comes together and has an elastic quality but is still a bit runny. The dough it quite sticky, so you can coat your hands in flour and lift the dough from the bottom of the bowl and sprinkle more flour there then top the dough with a dusting of flour. You may wish to transfer to another bowl or leave it in the stand mixing bowl.