Choosing the right white chocolate for melting
Look carefully at the labels of the “white chocolate” that you find in the baking aisle at the grocery store. While many bars and chips will be true white chocolate— consisting of cocoa butter, sugar, and milk solids— some are not. Synthetic white chocolate substitutes are made with palm oil or something similar and do not contain any cocoa butter. While they may be okay to use in baking, these substitutes will not melt well.
Make sure that what you buy is labeled as “white chocolate” and has “cocoa butter” listed in the ingredients. USDA regulations require that only true white chocolate can be labeled as such.