I use a double boiler in a number of recipes, especially ones that contain cream cheese, since cream cheese would be burned if melted in a saucepan on the stove-top. “Mom’s Cream Cheese Frosting” uses a double boiler, as well as the “Gluten-Free Cheesecake.” Another thing that you would want to melt in a double-boiler is chocolate, which can burn fairly easily.
Though there are actual ‘double boilers’ you can buy, there is a simpler, less-expensive, homemade version:
Place water in a small saucepan, at least an inch thick, so that the water will not boil away. Place a stainless steel bowl on top of the saucepan, big enough that it won’t touch the water. Put whatever you need to melt/cook in the bowl on top and heat the burner to high.
The water will boil underneath the bowl, and the steam will rise and heat the bowl, therefore slowly and evenly heating the contents. Cook/melt contents for as long as the recipe says. In the case of the cream cheese or butter (butter can melt in a microwave or a saucepan on medium low heat, but you can also use a double boiler), only until the cream cheese is soft enough to blend or butter is melted.