In a large bowl, mix the butter and powdered sugar with a hand mixer until crumbly. Add the vanilla and peppermint extracts and salt, and mix until smooth. It will seem like it takes forever, but it will happen after a few minutes. Depending on your hand mixer, you can turn it up to medium or medium-high speed and the mixture will come together faster.
Scoop 1-tablespoon balls of cold dough and place them on a cookie sheet lined with wax paper. Refrigerate for at least another 30 minutes.
When you're ready to dip the truffles, melt the melting chocolate according to the package directions, and line a cookie sheet with waxed paper. Remove the truffles from the refrigerator and roll into smooth balls. These soften pretty quickly, so it's best to keep them in the refrigerator and remove 4 or 5 at a time to dip.
Dip each truffle in the melted chocolate, tapping off any excess, and place them on the prepared cookie sheet. Sprinkle with sprinkles if using. Return the truffles to the refrigerator to harden. Store in an airtight container in the refrigerator; they soften quickly. The truffles will keep for several days when kept cold.