Set up double boiler over barely simmering water.
Add chocolate chips to bowl/double boiler and slowly melt.
Once melted, add sugar, salt and vanilla. Whisk until fully blended.
Remove melted chocolate from the heat.
Whisk in sour cream until fully blended. Ganache will be very loose while it is warm...but will set up and thicken as it cools.
Place warm bowl of ganache in refrigerator for at least 30 minutes to cool it down.
Remove ganache from fridge. Check to see that it's firmed up a bit. It will still be quite soft (not like a butter cream or cream cheese frosting). Whisk it again. If it's still super runny, pop it back into the fridge or even freezer to speed up the cooling process.
Once ready, place the frosting into a piping back fitted with any tip you desire and frost the cupcakes.
If desired, dust the tops of the cupcakes with metallic sprinkles. I dip a small paintbrush into the dust and tap it above the cakes.