Add the softened butter and sugar to the bowl of a mixer and cream until fluffy, about 3-5 minutes.
While the butter and sugar are creaming, in a small bowl add the dry ingredients and fluff mix with a fork.
Add the eggs and the vanilla to the creamed butter and sugar, mixing on low until combined. Next add the buttermilk and mix on low to incorporate.
Lastly, add the dry ingredients to the mixer bowl and blend until just combined, turn the mixer off and stir by hand with a large spatula a couple times to make sure everything has come together.
With a soup spoon, drop mounds of dough (a generous tablespoon and a half or so) onto a cookie sheet and bake for about 12-15 minutes, until very barely golden. Remove the cookies to a rack to cool.
While the cookies are cooling, combine the icing ingredients in a small bowl until it’s lump-free and smooth. Top the cooled cookies with a spoonful, spreading the icing with the back of a spoon or offset spatula.
Let the icing set up and serve. Store in an airtight container.