Add the chopped up white chocolate to a microwave safe bowl, top with the heavy cream, sweetened condensed milk, and evaporated milk, and microwave in 30 second intervals until fully melted, stirring in between every time.
8 oz white chocolate bar or chips, ½ cup heavy cream, ⅓ cup evaporated milk, ⅓ cup sweetened condensed milk
Whisk vigorously to get everything emulsified properly and use in your white chocolate mocha drinks.
Notes
If you do not have a microwave you can make this white chocolate mocha sauce over a double boiler.