This one is from The Essence of Chocolate and I always get rave reviews everytime I take it somewhere. It's not overly sweet, definitely more of a "grown-up" treat with sea salt and cacao nibs.
1 cup flour
3/4 cup unsweetened cocoa powder
6 tablespoons cacao nibs
1 teapsoon fine or coarse sea salt
12 tablespoons unsalted butter, at room temperature
1/2 cup sugar
1 teaspoon vanilla extract
Preheat oven to 325 degrees. Line two baking sheets with parchment paper or silicone liners.
Combine the flour and cocoa powder in a small bowl. Combine the nibs and sea salt in a separate bowl (I pulse a few times in my spice grinder.)
Beat butter and sugar until fluffy. Add the vanilla extract. Add about 1/2 of the flour-cocoa mixture and mix well, then add the remaining flour-cocoa mixture. Increase mixer speed to medium and beat for 1 to 2 minutes. Mix in the salt-nibs mixture by hand.
Lightly flour a work surface and rolling pin, or flatten the dough and place it between 2 large pieces of plastic wrap; roll the dough into a square 1/4 inch thick.
Using a knife or a cookie cutter, cut into 1-by-2 1/2-inch rectangles or other desired shape, and place the cookies about 1 inch apart on the baking sheets. Bake for 7 minutes, then rotate the baking sheets from top to bottom and front to back; bake for 8 minutes or until their aroma is apparent and the cookie bottoms are crisp. Let them cool on the sheets for 5 minutes, then transfer to a wire rack to cool completely.