Preheat the oven to 350°Fahrenheit/175°Celsius. Place 6 cupcake liners in a cupcake pan.
In a large bowl with a hand held mixer or in a stand mixer fitted with the paddle attachment, combine the flour, baking powder, salt and sugar.
Add the room temperature butter and mix on low speed until the butter and dry ingredients almost looks like clumpy sand.
In a large jug, whisk together the egg with buttermilk, vanilla bean paste and oil.
Pour the wet ingredients into the dry ingredients and mix on low speed until combined.
Using a tablespoon or a medium cookie scoop, scoop out 1 ½ tablespoons of cupcake batter to spoon batter into the liners. This should fill up 6 cupcake liners, about ½ way full.
Bake for 18-20 minutes. Let the cupcakes cool in the pan for 10 minutes before removing and letting them cool completely on a wire cooling rack.
In a stand mixer fitted with the paddle attachment, or in a large bowl with a hand held mixer, combine the room temperature butter with the confectioners' sugar on low speed.
Increase the speed to medium-high and beat for 2-3 minutes, until light and fluffy.
Add the vanilla and salt, beating once more. If the frosting isn't as creamy as you would like, add in the heavy cream and beat on medium speed until spreadable.
Notes
My recipes have been developed and tested in cups and metric grams. I highly recommend using a weighing scale and measuring out your ingredients the metric way.I make sure that all of my ingredients are at room temperature before I start the recipe, so pull out all of the ingredients before you start baking.Butter: I use European style butter, like Kerry Gold, in my recipes. This will make your frosting much creamier and richer.Salt: If you don’t have kosher salt, halve the amount of salt called for in the recipe. 1 teaspoon kosher salt = ½ teaspoon fine salt. Please note, I am using Diamond Crystal kosher salt and not Morton Salt, which is far too salty for this recipe. Buttermilk: You can swap out buttermilk for sour cream or full fat yogurt.Vanilla Bean Paste: feel free to use vanilla extra if you don't have bean paste. Storage: Keep in an airtight container in the fridge for up to 5 days. Let it come to room temperature before eating.