A bain-marie is a water bath. We use them all the time in pastry to melt things or gently cook things. All you need is a pot and a metal or heatproof glass bowl that can rest on top of it. Pour at least 3 inches of water in the pot and bring it to a simmer. Place the bowl on top of that and voila! Instant bain-marie. The Soy Ganache can be stored in an airtight container in the refrigerator for up to 3 days. If refrigerated, melt it in a bain-marie or in the microwave before using. The Vegan Marshmallow recipe makes about 1 cup, more marshmallow than you need for the cupcakes, but it's hard to whip up a smaller amount. If your mixer's whisk isn't engaging with the aquafaba because there isn't enough in the bowl, consider doubling the recipe.