By peppermint liqueur you mean mint-flavoured vodka, not an ethanol-with-syrup thing, right? Would be too sweet, while if it's vodka, I'm definitely trying this some time soon.
Anyway, my recent discovery: good old White Russian is also delicious if milk is hot and is just as good for sore throat as traditional hot milk-and-honey, just much, much tastier.
Not really to be honest, I tried both Minttu and liqueur and both work great, if you use the liqueur though you have to cut down on the sugar while making the hot chocolate.