Using a handheld or stand mixer fitted with the paddle attachment, beat the butter on medium speed until creamy. Add the peanut butter, vanilla, and salt, and beat until smooth and combined.
Add the icing sugar, and beat on low until combined. The mixture will be crumbly, but you should be able to roll into balls.
Roll the dough mixture into 1-inch balls (about 0.5oz each), and place on a baking tray lined with parchment paper or a silicone mat. You should have about 40 - 45 balls. Refrigerate until firm - about 1 hour.
Add the dark chocolate to a microwave-safe bowl, and heat in 30 second intervals, stirring after each one, until melted and smooth. Leave to cool for 5 minutes.
Repeat with the milk chocolate.
Dip each peanut butter ball into the melted dark chocolate, and place back onto the baking tray. Drizzle with the milk chocolate. Allow to set in the fridge before serving.
Notes
You may use any type of chocolate you want, you don't have to use dark!Truffles can be kept in an airtight container, layered between parchment or wax paper, in the fridge for up to 1 week. They also freeze well for up to 2 months. Thaw overnight in the fridge.