Preheat oven to 350°F. Line a regular cupcake pan with paper liners or grease with nonstick baking spray.
In a bowl, combine eggs, egg yolks, and 1/2 cup of buttermilk. Set aside.
In the bowl of a stand mixer fitted with a paddle attachment, or in a large bowl if mixing with hand-held mixer, add flour, sugar, baking soda, baking powder, salt, cubed butter and remaining 1 cup buttermilk.
Beat on low speed until moistened, then increase speed to high and beat until light and creamy, about 3-4 minutes, scraping down the bowl once or twice.
Add egg mixture in 2 additions, mixing after each.
Fill cupcake liners no more than 2/3 full. Bake until tops of cupcakes are barely golden and bounce back when gently pressed, 16-18 minutes.
Let cool in pan for a few minutes, than remove to a wire rack to cool completely.