Melt dark chocolates and butter together; set aside
In the bowl of a stand mixer, beat eggs and sugar until light and fluffy; 8-10 minutes
Gently fold in espresso and vanilla
Carefully combine egg and chocolate mixtures
In a separate bowl, whisk together remaining ingredients, except the icing sugar
Combine dry and wet ingredients until just combined
Divide dough into four equal parts and roll each section into a log about 12" long.
Roll each log in icing sugar. Set in fridge to chill, at least 30 minutes
Preheat oven to 325 F
Slice each log equally into 10-12 slices
Bake on a lined cookie tray approximately 10 minutes. Do not overbake.
If you are not baking the cookies immediately, wrap tightly in plastic wrap and place inside a zip top bag. Can be kept in the fridge up to 3 days or freezer up to a month. Bake cookies from frozen.