With an electric mixer, cream the butter with the sugar until the mixture is light and fluffy. Add in mint extract.
Add flour, baking powder and salt. Mix until it forms a dough.
Divide the dough in half. On a sheet of wax paper, form each half into an 8-inch log. Gently press the log so that it's more oval than round. Chill the logs, wrapped in the wax paper, for at least 2 hours or overnight. (If you’re pressed for time, 30 minutes in the freezer works well too!)
Heat the oven to 300°F.
Cut the logs into 1/4-inch-thick slices with a sharp knife.
Arrange the slices 2 inches apart on parchment-lined baking sheets.
Bake the cookies on the top rack of the oven for 22-24 minutes.
Transfer to wire racks to cool.
Heat chocolate in microwave for 1 minute, Stir gently and continue heating in 15 second increments until smooth. Pair 2 similarly shaped cookie ovals together. Spoon about 1 tsp of melted chocolate onto the flat side of one cookie, then gently press the flat side of the other cookie on top. Set on a cooling rack until chocolate is cooled. Continue with remaining cookies until you have them all sandwiched in pairs.
Dip 1/2 to 3/4 of the sandwiched cookies in chocolate, then set on wax paper to cool. Melt white chocolate and drizzle on top, if desired.
OR... you could leave the cookie ovals separate and dip each one in chocolate, much like I did for my Mint Chocolate Cookies here. Both are amazing and both taste like Mint Milanos!
*If you want more of a subtle mint flavor, leave the extract out of the cookie dough and just add it to the chocolate, as opposed to adding it in both places.
**You can use chocolate chips + 1 tsp coconut oil or shortening mixed in in place of melting chocolate.