1 c unsalted butter, melted
3/4 c sugar
1 t vanilla
1 c semisweet chocolate chips, melted
1 1/2 c flour-2 c flour
3/4 c cocoa powder
1/2 t salt
1/2 t baking soda
1/2 c unsalted butter, softened
1 2/3 c powdered sugar
1 t vanilla
1 T milk
pinch of salt
Whisk together the butter and sugar. Whisk in the vanilla and chocolate. Add the egg and whisk until thoroughly combined.
In another bowl, stir together the flour, cocoa powder, salt, and baking soda until well mixed. Fold the flour mixture into the chocolate mixture. It should be the texture of play-doh. (I had to add more flour to get this texture, about another 1/4 cup) Let the dough sit at room temperature for about 1 hour to firm up.
Roll the dough in parchment paper, and roll to make a 2 1/2 inch in diameter log. Refrigerate for at least 2 hour, until firm, rolling every so often to stop one side being squared off.
Preheat oven to 325. Line a baking sheet with parchment paper. Cut the dough into 1/4 inch slices. Bake for 16-25 minutes, checking them frequently after 16 minutes. (Mine went for about 19) They should be firm to the touch. Allow them to cool, then frost and make sandwiches.
Beat the butter for about a minute. Add in the vanilla and powdered sugar and beat until smooth. Add in the milk and salt, then fill the cookies. Serve.