Preheat the oven to 350°F/175°C. Line a 12-cup pan with cupcake liners. This recipe makes 13-14 cupcakes.
In a medium bowl, whisk together the flour, baking powder and salt.
1 ¾ cups all purpose flour, 1 ½ teaspoons baking powder, ½ teaspoon kosher salt
In a small bowl, combine the ½ cup of sugar and cinnamon for the cinnamon sugar swirl.
½ cup sugar, 1 ½ teaspoons ground cinnamon
In a stand mixer with the paddle attachment, beat the butter and sugar together on medium-high speed for 2 minutes. It should become light and fluffy.
½ cup unsalted butter, 1 cup sugar
Add the eggs and vanilla extract, then beat again on medium speed
2 large eggs, 2 teaspoons vanilla extract
Add in the sour cream, beating on medium-low speed until well combined
½ cup sour cream
With the mixer running on your lowest speed, add the dry ingredients
With the mixer still running on low, slowly pour in the buttermilk. Stop the mixer.
½ cup buttermilk
Use an ice cream scooper to fill each cupcake liner with 1 tablespoon of batter. Sprinkle over 1 teaspoon of cinnamon sugar, then another tablespoon of batter. Take a toothpick and swirl the batter together then sprinkle over another teaspoon of cinnamon sugar.
Bake for 20-23 minutes. A toothpick inserted will come out clean with no crumbs. Let cool completely. Your cupcakes might have split at the top, almost like a muffin - this is ok!
Make Frosting
In a stand mixer fitted with the paddle attachment, beat the butter and brown sugar together on low speed until well combined.
2 sticks unsalted butter, ½ cup light brown sugar
Slowly start adding the confectioners’s sugar on your lowest speed
3 cups confectioners' sugar
Increase the speed to medium-high and beat for a 2 minutes until it becomes very thick.
Stop the mixer and add the salt, vanilla, and cinnamon in to the bowl. Beat on medium-high speed for another 2 minutes.
Turn the mixer to your lowest speed and pour in the heavy cream. Beat until it becomes very creamy and spreadable.
¼ cup heavy cream
Notes
My recipes have been developed and tested in metric grams. I highly recommend using a weighing scale and measuring out your ingredients the metric way. I have provided a conversion to US cups but please note that I haven’t tested the recipe with this method. Just click on ‘US CUSTOMARY’ above the list of ingredients. Ingredients: 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. Note that I am using kosher salt like Diamond Crystal kosher salt and not Morton salt - Morton salt is far too coarse and salty for this recipe! Buttermilk: If you don’t have buttermilk you can substitute sour cream. Storage: Store the cupcakes in the fridge for up to 5 days. Let them sit at room temperature for 30 minutes before eating.