Heat the whipping cream and butter together just to a simmer, then add chocolate. Remove from heat while chocolate melts. Add flavoring. Stir until glossy and pour into a chilled bowl. Set aside until firm.
Once firm, use a small melon baller and scoop ganache out. Roll by hand, using cocoa powder to reduce stickiness. Chill until firm.
Melt 6 ounces bittersweet chocolate with 2 tablespoons solid vegetable shortening in the microwave for about 1 minute. Stir until melted; microwave additional seconds as needed. Drop each ball individually into chocolate, roll with a fork until coated, then use the fork to lift out and place on parchment paper. Chill and keep refrigerated.