In a microwave-safe bowl, add the butter, white chocolate chips, and pour the sweetened condensed milk right on top.
Microwave on high for one minute. Let the mixture stand for one minute and then stir. Continue to stir until everything is melted, this may take a few minutes, it will come together.
Let the ganache cool to room temperature, about 15 minutes. Cover with plastic wrap and place the bowl in the fridge until the ganache is set and no longer runny at all. It will be very thick and rollable. This will take about 2 to 3 hours.
When the ganache is set up, depending on what size you want the truffles, take about 1-3 teaspoons of the ganache and roll it between your hands to form a ball. Immediately roll the ball in sprinkles of your choice. (Pictured are white nonpareils) Continue until all the ganache is used up, enjoy!