In a large bowl, beat the butter, sugar and vanilla until creamy, about 3 minutes. add the cocoa and blend well.add the salt, then gradually add the flour, blending till smooth.
On a lightly floured surface, roll the dough to about 1/2" thickness.
Use a cookie cutter to cut out the cookies and transfer them to an ungreased cookie sheet. the scraps can be gathered and rerolled.
Bake the cookies for about 20 minutes or until just firm.
Cool slightly on sheet, then transfer them to a wire rack to cool completely.
GLAZE: In a small saucepan, melt the butter over low heat, stir in cocoa and 1/4 cup of water. Cook over low heat, stirring constantly, until the mixture thickens and becomes smooth. Remove from the heat, and stir in vanilla. Gradually add the sugar, and salt stirring with a whisk until smooth. If need, add more water, 1 tsp at a time to achieve a spreadable consistency.
To dip the cookies, tip the pan of chocolate toward you and dip about half of each cookie into the glaze.
Place on a wax paper lined rack until the glaze is set.
Store the cookies in layer, seperated by waxed paper.
In tightly covered container in a cool, but not cold place.