Heat oven to 350. Place 1 T. coffee granules and 2 T. hot water in medium bowl; stir until dissolved. Stir in brownie mix, 1/2 cup butter, flour and egg.
Place coarse sugar into small bowl. Shape dough into 1 inch balls; roll in sugar. Place 2 inches apart onto ungreased cookie sheets. Bake for 8 to 10 minutes or until set. Cool 2 minutes; remove from cookie sheets. Cool completely.
Place 2 t. coffee granules and 2 T. hot water in small cup; stir until dissolved. Beat 1/4 cup butter in medium bowl at medium speed until creamy. Gradually add powdered sugar alternately with dissolved coffee granules, scraping bowl often, until well mixed. Stir in corn syrup.
Spread 1 t. buttercream onto bottom-side of 1 cookie. Top with another cookie, bottom-side down.