In the bowl of a stand mixer beat the butter and sugar together on high speed for 5 minutes, scraping the bowl sides and bottom once or twice. Add the egg and vanilla and beat it on high for a further-2-4 minutes. The mixture should be very light and creamy and doubled in volume.
For Chocolate Covered Cookies: Chop 8 oz of good quality dark chocolate into small pieces. Place in a microwaveable bowl and microwave for 30 seconds on high. Stir the chocolate and microwave for a further 30 seconds. Stir and continue to microwave in short bursts until the chocolate is melted through. (See note for white chocolate) Dip one side of the top cookies in the chocolate and place on a tray to dry. Once the chocolate has set, spread jam on the lower cookie and top with a chocolate covered cookie.
Note: For a more sophisticated flavor, add a teaspoon or two of a sweet liquor to the jam before spreading it.
To use white chocolate for the icing, use fresh white chocolate. Melt it at 50% power in 15 second bursts until it has melted. White chocolate burns easily and will seize if over-heated.
Finished Cookies can be frozen for up to two weeks