Preheat the oven to 350F. Line a muffin pan with cupcake/muffin liners.
In a small bowl, combine the milk and vinegar. Set aside.
In a large bowl, using a hand-mixer, beat together the melted butter and sugar for 30 seconds on medium speed. Add the remaining wet ingredients (milk and vinegar mixture, eggs, and vanilla extract) and beat for 30 seconds on low-medium speed.
Add the dry ingredients to a sifter/sieve/strainer. Sift the dry ingredients into the wet ingredients.
On low-medium speed (so the flour doesn't fly all over the counter), carefully beat the dry ingredients into the wet ingredients for about 30 seconds. Don't over-beat the batter--just mix until the ingredients are combined.
Scoop the batter into the individual liners in the muffin pan. Don't overfill the individual liners with batter--about 1/4-1/3 of the way full is ideal. If you have any extra batter, go back and add a small amount to each cupcake, or if you don't want any "muffin tops" on your cupcakes, bake the extra batter as extra cupcakes.
Reduce the oven temperature to 325F. Bake the cupcakes for about 20-22 minutes, until the the tops are firm and have a bit of a "spring" when touched.
Allow the cupcakes to fully cool before frosting.
For the Buttercream Frosting:
Using a hand-mixer, beat the butter, vanilla extract, and pinch of salt on medium speed until it's creamy and slightly fluffy.
Add the powdered sugar, one cup at a time, beating the sugar and butter together. Continue until all the sugar is added.
Finally, add the milk, a splash at a time, beating the frosting until you reach the desired consistency. Less milk results in a thicker frosting. More milk results in a fluffier frosting. Use as many splashes of milk as needed.
Frost each cooled cupcake with the buttercream frosting. I use an ice cream scooper to scoop and drop the frosting on the cupcakes, and then level and spread the frosting with a knife.
The frosted cupcakes can be kept at room temperature for several hours. Store any leftover cupcakes in the fridge.
Notes
Depending on how much you fill the muffin pan, you'll probably get between 12-15 cupcakes (12 if you fill them 1/3 way full, and the cupcakes with have "muffin tops"; 15 if you don't want the "muffin top" look)*Einkorn is known as the oldest variety of wheat making it an ancient grain. The ancient grain is believed to have originated in the Tigris-Euphrates region and is possibly the main grain referenced in the earliest accounts of the Bible. To put it simply, einkorn is the wheat men were eating in the earliest days before modern-day wheat varieties. While modern wheat has undergone hybridization, einkorn still holds true to its original properties. Einkorn is slowly gaining popularity, but is still grown in only a few regions in Europe.The sweet, ancient grain has a lighter texture and taste than modern-day wheat, and contains a more favorable gluten ratio. People with minor gluten sensitives may be able to consume einkorn without the issues associated with whole wheat due the lack of D-genome, however, einkorn is not gluten-free. Einkorn looks and tastes similar to white flour. Einkorn is sold in some health food stores and online.**I believe organic corn starch can be substituted for the arrowroot flour/starch. Muffin Pan: I use a dark, non-stick muffin pan. If you're using a light, ceramic pan you may need to cook the cupcakes a bit longer than recommended or even keep the oven temperature at a 350F. Sprinkles? I used crushed dehydrated strawberries in the photos. I also like India Tree company for sprinkles and natural dyes.