Place the milk, mint leaves, and vanilla pod and scrapings in a large, heavy-bottomed saucepan placed over medium heat. Slowly heat to just below a simmer, until steamy, stirring frequently to prevent scorching the milk. Remove from the heat and steep 10 minutes. Strain the milk through a fine mesh sieve and into a large bowl, squeezing all the good stuff out of the mint leaves. Discard the leaves. Meanwhile, sift the cocoa into a medium bowl with the sugar and salt. Add enough of the hot milk to the cocoa mixture and whisk to form a smooth paste (this prevents the cocoa from clumping), then whisk in the rest of the milk and return to the pot placed over medium heat. Warm the cocoa until hot to your liking, stirring to prevent scorching, and adding enough peppermint extract until you like the flavor. Ladle into mugs and top with matcha marshmallows.
The hot cocoa can be made up to several days ahead and refrigerated; heat before serving.
Add a splash of bourbon or whiskey to each cup if you want to booze it up!If you don't have marshmallows on hand and need a quick matcha fix, whip together 3/4 cup heavy cream, 1 tablespoon sugar, and 2 teaspoons matcha powder until soft peaks form for a quick topping.Nutritional values are based on one of four drinks.