If baking immediately, turn oven to 350. (disregard if you are freezing).
Cream butter until light & fluffy, then add powdered sugar and mix completely. Stir in salt, vanilla & cocoa powder. Mix until completely mixed, w/ consistency of thick icing/frosting. Add flour & mix just until combined. Don't mix too long!
Form dough into a ball. Knead a few times, then flatten into a disk between 1/2" - 1" thick. Cover in plastic wrap then place in freezer for 15 minutes.
Remove dough from freezer. Roll until very thin (1/8") on floured surface. Cut cookies using 1.5" cutter or rim of a small glass.
Place cookies on a baking sheet & bake for 10 minutes.
Allow to cool completely on a wire rack. While cooling, start prep of chocolate coating.
Chop baking chocolate into very small, thin pieces. Place in a glass measuring cup along w/ the oil & microwave 15-20 seconds at a time until totally melted. Stir in peppermint extract.
Drop cookies, one at a time into the coating. Turn to coat entirely. Place on parchment paper to set. (&/or place into refrigerator or freezer to set).