Mix butter and sugar with a wooden spoon, the beat in the egg yolk and extract. Sift together the flour and a pinch of salt and add to the sugar mixture. Add in chocolate bits, and stir to combine. Wrap dough in plastic and chill for 30 minutes.
After your dough is chilled, roll it out and, using a cookie-cutter or glass, cut out your shapes.
Bake at 375 for 10 to 15 minutes. Let cool completely on a wire rack.
For the Ganache:
In a saucepan over low heat, melt cream and chocolate. Stir occasionally, until smooth. Remove pan from heat and let cool, then chill in the refridgerator until the mixtures reaches a spreadable consistency.
Spread ganace over half of the cookies and top with another cookie. Dust with powdered sugar.