Preheat the oven to 350°F (177°C) and line a standard cupcake pan with 6 paper liners. Then, combine the all-purpose flour, baking powder, and Kosher salt in a small bowl. Set aside.
Add the softened unsalted butter and granulated sugar to a medium mixing bowl. Using a hand mixer with beaters, cream the butter and sugar until it's very light and fluffy, about 3-4 minutes. Scrape down the sides of the bowl with a rubber spatula halfway through to ensure there are no streaks. Then, mix in the egg and vanilla extract until smooth.
Add the dry ingredients (flour, baking powder, salt) to the wet ingredients. Mix until the batter is about 75% combined. Then, add the whole milk and neutral oil. Mix just until the batter comes together and there are no more streaks of flour. Don't over-mix because it can make the cupcakes dense!
Using a cupcake scoop, evenly divide the batter between the cupcake liners. They should be about ⅔ of the way full. Bake the cupcakes for 16-18 minutes, or until an inserted toothpick has just a few moist crumbs. Let the cupcakes cool in the pan for about 5 minutes. Then, transfer the cupcakes to a wire rack to cool completely, about 1 hour.