Sift the flour , cocoa powder, baking soda, and salt into a med. bowl and set aside In a large bowl, using an electric mixer on low speed, beat the butter and sugar until blended and lightened in color, about 2 min.
Stop the mixer and scrape the sides of the bowl as needed during mixing.
Add the egg and vanilla and mix until blended, about 1 minute.
Add the flour mixture and mix well.
Refrigerate for about 20 min.( I did it for 10 and it was fine)
Preheat oven to 325*.
Roll heaping tbsp (3 level tbsp each) of dough between the palms of your hands into smooth 1 1/2 inch balls, and place them 3 1/2 inches apart on baking sheets. Flatten down the cookies with your hand to 2 1/2 to 3 inch rounds. The measurements are for those who like to have them. I just go for it!
Bake the cookies for about 15 min.
Transfer to a wire rack and cool.
For the Chocolate coating:
Put the chocolates and the oil in a heatproof container or the top of a double boiler, and place it over, but not touching, a saucepan of barely simmering water.
Stir until the chocolate is melted and smooth.
Remove from the water and let the chocolate coating cool and thicken slightly.
Spoon the chocolate coating over the top half of the cookies, using 1 tbsp per cookie.
Use the back of the spoon to spread evenly and coat them completely.
Let the cookies set at room temperature until set.
Make the filling:
In a large bowl, beat the butter, powdered sugar, vanill and peppermint extract until smoothly blended, about 1 min.
The filling will be quite thick.
Turn the plain cookies bottom side up.
Spread on a well rounded tbsp of filling in the center of each, carefully place the bottom of a chocolate coated cookie on the frosting, and gently press the cookie to spread the filling into an even layer.
Wrap each cookie in plastic wrap and refrigerate for at least 2 hours(if you can wait that long).
The wrapped cookies can last up to 4 days stored in the refrigerator.
You can omit the peppermint filling and serve them with just the chocolate coating on them.