Thoroughly muddle blackberries in a cocktail shaker. Add lemon juice, simple syrup, amaro, whiskey, and 1 cup ice cubes. Cover and shake well. Pour contents into a glass and add a lemon slice.
*Find Ramazzotti amaro (an Italian bitters liqueur) at well-stocked liquor stores, and Slow Hand Six Woods whiskey at holidaywinecellar.com.