Combine powdered sugar, sweetened condensed milk, butter, salt and vanilla in a large bowl and blend thick and combined. Gently mix in 1 ½ cups of crushed peppermint candy until fully incorporated.
Roll filling into ¾-inch round balls. Place on a baking sheet lined with parchment paper and chill or freeze for at least 30 minutes.
When you’re ready to dip the candies, melt 12 ounces of semisweet chocolate in a double boiler over low heat or in a microwave. If using a microwave, heat chocolate for 30 seconds at 50 percent power, then stir. Continue microwaving in 15-second increments at 50 percent power until the chocolate is completely melted.
Be careful not to overheat the chocolate or it will seize and clump, and you’ll be unable to use it for dipping. If necessary, thin the chocolate with vegetable oil, a teaspoon at a time, until it’s a good dipping consistency.
Working in small batches, dip chilled candies in chocolate. The best way to do this is to lay a candy on the tines of a fork. Lower the fork into the warm chocolate, until the candy is submerged. Then, raise the fork, allowing the extra chocolate to drip through the tines. Tap the fork on the edge of the dipping bowl to remove any excess chocolate. Then gently slide the dipped candy onto baking sheet lined with parchment.
Before the chocolate has time to cool and set, sprinkle candies with remaining peppermint pieces.