2 sticks of Butter, softened to room temperature (the regular ol' salted stuff)
1 - 2 TBLS Corn syrup
4 cups Powdered sugar (I buy huge bags at Sam's Club, but a regular small bag is fine)
1 TSP Vanilla (nothing fancy, I buy a big bottle of that at Sam's too)
2 TBLS Milk (I use 2%, whole would be great too. I don't recommend skim)
Put butter, milk, and vanilla in the bowl of a stand mixer.
Mix on low speed until it just starts to come together, about a minute. Scrape the sides of the bowl with a spatula. Increase to medium low speed and beat for about another minute. It should be almost combined but there will still be a bit of liquid at the bottom.
Increase mixer speed to medium high and beat for about another or minute or so. Add powdered sugar. Beat on low speed until sugar is just barely incorporated. Scrape down the sides of the bowl, and increase speed slowly to medium. Beat for about a minute.
At this point, you want to check your consistency. This is very important because if your frosting is too thick, it will not spread well. If your spatula does not glide through the frosting, add about a tablespoon of corn syrup and beat on medium for about 30 seconds.
Add another tablespoon of corn syrup and beat on medium for 30 seconds. Repeat until the frosting seems to be of a good spreadable consistency. You don't want it too runny though, or it will just slide off the cake.
Once you get your frosting to a good, spreadable consistency, increase mixer speed to medium high and beat for one minute. This will get your frosting nice and fluffy.
Here's how to take your frosting a step further:
With an offset spatula, put a good - size blob of frosting on your cupcake.
Use your spatula to get it nice and flat. It's okay if it's not perfectly smooth, just make sure that it's spread to the edges of the cupcake.
Holding your spatula with it's edge along the side of your cupcake, give your cupcake a spin. This will take off the excess frosting and make your edges nice and flat.
Pour your favorite sprinkles onto a plate and roll the edges of the frosting in the sprinkles.