In a medium sized bowl cream together the butter, sugar and vanilla until light and fluffy. Add the egg and mix until a smooth paste forms.
Add the flour and mix until it is just starting to come together. Dump the dough onto the counter and press the dough into a ball.
Refrigerate the dough for 20 minutes.
Lightly flour a surface and roll the dough about ⅛ inch thick. Cut 2 inch circles in the dough.
Place the cookie dough rounds on a lined cookie sheet. Bake the cookies at 350° for 8-11 minutes or until the edges are golden brown.
Allow the cookies to cool to room temperature.
Heat the cream until it is just under a boil. Pour the cream on top of the chocolate and stir until a smooth ganache forms. Allow the ganache to thicken to a pipable consistency.
Spoon the ganache into a piping bag and pipe ganache onto half of the cookies. Place the other half of the cookies on top of the ganache filled cookies sandwiching the ganache.
The cookies will keep for up to 5 days at room temperature.