Preheat oven to 350F (175C) and line a 12-count muffin tin with paper liners. Set aside.
Combine butter and sugars in the bowl of a stand mixer (or in a large bowl -- and use an electric hand mixer) and beat on medium speed until well combined and light and fluffy.
Add egg and vanilla extract and beat well.
In a separate, medium-sized bowl, whisk together flour, baking soda, baking powder, and salt.
Remove butter/sugar mixture from stand mixer and use a spatula to gradually fold in about 1/4 of the flour mixture until just combined.
Add about 1/4 cup of the buttermilk and use spatula to fold in until just combined.
Continue to alternate until flour mixture and buttermilk are completely combined -- mix thoroughly but be sure not to over-mix or your cupcakes could end up dense and dry.
Fill cupcake liners 2/3-3/4 of the way full with batter (do not over-fill, if you have any leftover batter discard it) and bake on 350F (175C) for 17-18 minutes or until tops spring back when gently touched (the tops will be fairly flat, these do not puff up in the oven like muffins) and a toothpick inserted in the center comes out with a few moist crumbs or clean.
Allow cupcakes to cool completely in pans before frosting.
Chocolate Buttercream Frosting
In a microwave-safe bowl, microwave chocolate chips at 15 second intervals, stirring between intervals, until chips are completely melted. Set aside and allow to cool slightly (about 10 minutes, stirring occasionally).
Cream room temperature butter with an electric mixer. Stir in slightly cooled chocolate and beat well.
Gradually add sugar, scraping down the sides and bottom of bowl occasionally.
Sprinkle in salt and vanilla extract, stir well.
Gradually add heavy cream, increase speed to high and beat for 1 minute, pausing halfway through to scrape down sides of bowl.
Spoon frosting into a piping bag fitted with tip of choice (I used a large French tip) and pipe on cooled cupcakes.
¹If you don't want to use the chocolate frosting listed, try one of my other frosting recipes: