Place melted butter in a large bowl and let cool. With an electric mixer on medium to high speed, beat in eggs, one at a time. Beat in bourbon, if you like, and vanilla. Beat in sugars until well combined. Gradually beat in flour and salt until well combined.
Cover and chill dough at least 2 hours or until firm enough to scoop.
Preheat waffle baker. Drop dough from a small (1 tablespoon) cookie scoop, or drop by rounded teaspoonfuls into center of each waffle grid; close lid. (Make about 4 cookies at a time, leaving about 2 inches between dough mounds.) Cook on medium heat for 3 minutes or until cookies are golden brown. Using a fork, transfer cookies to a wire rack; cool. Repeat with remaining batter. If you like, sprinkle lightly with powdered sugar. Store in an airtight container at room temperature for up to 2 days. Makes about 25 cookies.