Cacao nibs are bits of roasted cacao beans, the primary raw ingredient used to make chocolate. Look for them in specialty or gourmet grocery stores.
Preheat oven to 325°. In a large bowl, use a mixer to beat together butter and sugar until light and fluffy. Add vanilla, salt, espresso grounds, and Kahlúa. Beat to combine. Add flour and cacao nibs and mix until well blended.
Form dough into two 1 1/2-inch-thick logs, cover with plastic wrap or wax paper, and chill at least 2 hours or overnight.
Cut chilled dough into 1/4-inch-thick slices and lay slightly apart on ungreased cookie sheets. Bake until cookies are browned on the bottom but not the top, 15 to 20 minutes. Transfer to a rack to cool.
Note: Nutritional analysis is per cookie.
Servings Makes 3 dozen cookies (serving size: 1 cookie)
* Percent Daily Values are based on a 2,000 calorie diet. Your daily value may be higher or lower depending on your calorie needs.