Preheat oven to 350ºF. Prepare a baking sheet by lining with parchment paper.
Cream together butter, powdered sugar, and vanilla in a large mixing bowl with an electric mixer until smooth.
Add in the cocoa powder and blend well, scraping the sides of the bowl as needed. Add flour and salt, beat until well combined. The dough will most likely not form a ball at this point. Use your hands to press the dough together into a ball before rolling out.
Roll the dough out onto a lightly floured surface to about 1/2 inch thickness. Use 2 inch cookie cutters to cut out cookies. Place on a parchment lined or ungreased cookie sheet.
Bake for 15-20 minutes until crisp. Cool on a cooling rack.
Chocolate Glaze
In a sauce pan over low heat, melt the butter, add in the cocoa powder and water, stir until smooth. Remove from heat and stir in the vanilla.
Stir in the powdered sugar a little at a time until the glaze is smooth.
If the glaze seems too thick, add more water 1 teaspoon at a time until the glaze is spoonable and not too thick.
Dip half of the cooled cookies into the glaze and place on a parchment lined baking sheet or cooling rack. Allow the glaze to set before serving.