To make double-strength coffee, measure 1/2 cup finely ground regular or decaffeinated espresso or other dark roast coffee into a cone lined with a paper coffee filter. Pour 1 1/2 to 2 cups hot water (190°F to 195°F) through filter into a large glass measuring cup (or put grounds in filter-plunger coffee pot, add water, let stand 2-3 minutes, then push plunger). Pour hot double-strength coffee over ice in a pitcher. When ice is almost melted, add liqueur, if desired. Pour into tall glasses, leaving room for a scoop of ice cream on top.