Place a rack in the center of your oven, and preheat your oven to broil. Place the marshmallows on a baking sheet. Broil the marshmallows for 1 to 2 minutes, just until they begin to brown and puff (see the photo in the post). Remove them from the oven and set them aside.
MAKE THE ICE CREAM BASE:
In a large saucepan, heat the whipping cream and half-and-half over medium heat. Once the mixture is warm, add the toasted marshmallows and stir until the marshmallows are melted. Whisk in the malt powder, vanilla and salt and stir until the malt is dissolved. Remove the pan from heat and let it cool to room temperature. Transfer the ice cream base to a covered plastic container and chill for at least 8 hours.
PROCESS THE ICE CREAM:
Remove the ice cream base from the refrigerator and give it a few whisks to reincorporate the ingredients. Resist the temptation to grab a straw right then and there and start sipping (because it's delicious!!) Follow your ice cream machine manufacturer's instructions for processing the ice cream. It usually takes 25 to 30 minutes for the ice cream to become creamy and frozen. Add in the brownie pieces just before you're about to turn off the machine, and let the machine mix them in for about a minute. Scrape the ice cream into a freezer-safe container and freeze for several hours, or until the ice cream is firm enough to eat. The ice cream will keep in the freezer for up to 2 weeks.
*For brownie pieces, I like to just make a package of box brownies from the store and crumble pieces from there. You'll use up about half a recipe.
*Most ice cream machines ask that you freeze the insert for 24 hours prior to processing your ice cream. This is what I recommend too.