Place your white chocolate chips and butter in a medium-sized, microwave-safe bowl and microwave for 30 seconds. Stir, and then return to microwave and continue to microwave at 15-second intervals (stirring between each one) until chocolate is melted and smooth.
Once chocolate is melted, stir in peanut butter until mixture is smooth.
Stir in vanilla extract and set aside.
In KitchenAid mixer (or with hand-mixer), stir your cream cheese on medium-speed until creamy.
Add peanut butter/white chocolate mixture and stir until well-combined, pausing occasionally to scrape down sides of the bowl.
Gradually add in powdered sugar, stirring until well-combined.
Line a cookie sheet with wax paper and drop dough by approximately 1 1/2 Tbsp-sized balls onto cookie sheet.
Once all of the truffle filling has been portioned, lightly roll each ball so that it is smooth (it will be greasy and won't make a smooth sphere).
Transfer the cookie sheet with the truffles to the fridge for 5-10 minutes.
Remove and roll into smooth, even balls (this will be much easier now that they are chilled, if they are still melty and difficult to shape, return to the fridge for an additional 5-10 minutes).
Place cookie sheet in freezer while you prepare your chocolate.
Melt dark chocolate according to instructions on package.
Remove truffles from freezer and, one by one, balance on the width of a butter knife blade (or set on the tines of a fork), pour chocolate overtop until evenly coated, and then use another knife to slide the truffle off of the knife blade and back onto the cookie sheet. Lightly sprinkle with sprinkles, if using.
Repeat until all truffles are coated in chocolate. Allow chocolate to set and harden before eating.
Keep uneaten truffles in an air-tight container in the refrigerator.