The blackberry spritz, from the james beard foundation, is a great example of how jams and fruit preserves can add wonderful flavor and velvety body to a cocktail. The original recipe calls for campari, a bitter citrus apritif. If you have a sweeter tooth, you can use aperol. Your jam or preserves can have seeds in it or not if it does, be sure to strain the drink through a fine wire mesh strainer before you serve it. Blackberry jam is specified, of course but its quite lovely with other berry jams as well.