Cookies:
Blend together flour, espresso powder and salt. Set aside.
Beat together butter and sugar until light and fluffy (about 2 minutes).
Add egg and beat for 2 minutes. Add vanilla and mix.
Stir in cocoa powder until just blended.
Slowly add flour mixture, mixing until just combined.
Scrape dough onto work surface and divide into two. Form each into disk; cover with plastic and refrigerate for 2 hours.
Preheat oven to 325°F; line 2 baking sheets with parchment paper, set aside.
Remove 1 disk from fridge and between sheets of parchment, roll out dough to thickness of about 3/16 x 10 inches.
Cut out dough using a 2-inch fluted rectangular cutter.
Place cookies on prepared sheets.
Bake 8 - 10 minutes. Cool.
Ganache:
In small pan combine whipping cream and espresso. Bring just to boil.
Remove from heat, and add chopped chocolates, whisk until smooth.
Chill 1/2 hour.
Spread about 1 tsp ganache onto bottom of each cookie, top with another cookie.
Dust with icing sugar.
NOTE: I usually double the ganache! I find that we like more filling in the cookies. And besides -- it is good right off the spoon, so there alone you need to double -- LOL.