A peppermint mocha latte is just a minty hot chocolate with the addition of espresso. You can get fancy and garnish with candy canes and the like, but this tastes just fine without all that fuss. Make it even easier on yourself by using a mint-flavored hot chocolate instead of trying to get the peppermint extract/cocoa ratio right.
Over medium heat, brew hot chocolate using milk instead of water. Once mixed, add the hot coffee. Pour into a mug and garnish with whipped cream if desired. If you want this extra minty, add a drop of peppermint extract.