This is a recipie adapted from Marg@Cayman Designs and it's really good:

14 oz sweetened condensed milk
1 Tb peppermint extract
6 c powdered sugar
24-32 oz semi-sweet chocolate chips
4-6 Tb shortening
(My sister also adds cocoa powder and vanilla to the filling)

Combine the sweetened condensed milk and peppermint extract. Slowly
add the powdered sugar and beat. Knead on a surface sprinkled with
more sugar until dough is stiff. (The stiffer the better when it
comes to the dipping part!) Add more sugar while kneading if the
dough is sticky. Roll 1/4 inch thick. Cut into approximately 1 1/4
to 1 1/2 inch circles. If they are much bigger than that, they fall
apart when you dip them. (You can also roll then into balls like the
filling of a chocolate candy.) Let the cut patties dry for at least 2
hours on each side. They really need to be dry. (In dry climates
liek Utah they only really need to dry for an hour on each side.)
Melt chocolate and shortening in a double boiler; stirring constantly
until smooth. Using 1 Tb of shortening for every 6oz of chocolate.
Keep the chocolate hot for dipping. Dip patties in melted chocolate.
You can use your fingers but it's a lot less messy to place the
patties on a fork and dip them in the chocolate, flipping the patty
over and dipping again to coat the other side. Shake off the excess
chocolate and then place on wax paper to harden. Makes about 24
patties.