Melt the chocolate in the microwave at 30 seconds increments or in the top of a double boiler. Add the sweetener and stir until smooth. Warm the cream in the microwave or another saucepan.
Add the warm cream to the melted chocolate. Transfer to a blender, rocket blender, or food processor (clean the bowl first). Process for a minute or two until thick and shiny. This step really insures a smooth ganache topping.
Spoon the ganache into a ziploc bag or piping bag (I buy these ones from Amazon) and pipe into the raspberries.
If you have some leftover you can chill it and then shape it into chocolate truffles.