Using an electric mixer on medium speed, beat butter, powdered sugar, and vanilla extract cinnamon in a large bowl until it just becomes light and fluffy, about 1 minute.

Add flour and on low speed, beat until the dough just starts to come together about 3 minutes.

Turn dough out onto a lightly floured surface and firmly press together to form a log. Divide the dough in half and form each piece of dough into a 6-inch log. Wrap in parchment paper and chill for at least 2 hours, up to three days.

Preheat oven to 350 degrees and line two baking sheets with parchment paper. Slice each log into ⅓-inch slices. You should have about 36 cookies.

Mix sugar and cinnamon in a small bow. Lightly brush the beaten egg on one side of a cookie and gently dip the egg-washed side into the cinnamon-sugar mixture. Evenly place on the parchment-lined baking sheets, sugar dipped side facing up. Repeat with the remaining cookies.

Bake until the bottom edges of the cookies just start to brown, 14-16 minutes. Allow cookies to cool and serve!