In a large, heavy skillet, fry bacon over medium-low heat, turning once, until partially cooked (should still be limp). Remove bacon to paper towels and drain all fat from pan. Return bacon to pan and sprinkle with 1/4 cup brown sugar. Cook over low heat, turning frequently, about 10 minutes, until bacon is well coated with sugar and very firm. Remove to a rack to cool. (Do not cool on paper towels). If any melted sugar remains in the pan, spoon it over the bacon.
Meanwhile, place shells in preheated 350ºF oven for 4 minutes to crisp. Remove and cool.
In a small bowl, with an electric mixer, beat mascarpone, remaining sugar, chocolate and coffee. In another bowl, beat heavy cream until stiff peaks form. Fold into chocolate mixture.
Spoon/Pipe about two teaspoons of chocolate mixture into each shell. Chop bacon into small pieces and sprinkle over chocolate. Serve immediately. Note: If not serving immediately, refrigerate filling and bacon so that shells stay crispy and crunchy once they're filled.