For the Lemon Cupcakes
- 21/4 cups all-purpose flour, spooned and leveled
- 11/2 teaspoons baking powder
- 1/2 teaspoon table salt
- 11/2 cups granulated sugar, divided
- 2 lemons, zested
- 3 eggs
- 11/2 teaspoons vanilla extract
- 1 teaspoon lemon extract
- 3/4 cup vegetable oil
- 1 cup full fat sour cream
- 1/2 lemon, juiced
For the Elderflower Swiss Meringue Buttercream
- 3 large egg whites
- 1 cup granulated sugar
- 11/2 cups unsalted butter, at room temperature
- 2-3 tablespoons elderflower liqueuer
- pinch salt
To Make the Lemon Cupcakes
Preheat oven to 350°F, and prepare 2 cupcake pans by coating with liners. In a medium to large sized mixing bowl, add the flour, baking powder, and salt, then whisk together to combine. In a separate bowl, add ½ cup of sugar and lemon zest, then rub together the sugar and zest until the sugar is all colored yellow and very fragrant, set aside.
In a stand mixer fitted with the paddle attachment, add eggs, sugar, lemon-zest-sugar, vanilla, and lemon extract. Beat on high for around 5 minutes, the mixture should look thick, fluffy, and be tripled in volume. Then, slowly drizzle in the oil. After all the oil has been added, beat for an additional minute.
On low, add the dry mixture to the stand mixer, mixing until just combined. Add in the sour cream and lemon juice, and mix only until the batter becomes smooth. Add the batter to the cupcake pans (filling each about 2/3 full), then bake in the oven for around 18 minutes, or until a toothpick comes out clean. Allow to cool completely before frosting.
To Make the Elderflower Swiss Meringue Buttercream
Place egg whites and sugar into a metal bowl and place over top of a pot of simmering water (ensuring the water is not touching the metal bowl). Whisk the mixture constantly until it reaches 165°F or 70°C. Remove from heat immediately and place into the stand mixer.
Using the whip attachment, turn the stand mixer onto high and beat the meringue for about 7 minutes. The meringue should have stiff peaks.
Turn the stand mixer to low and add in the butter 2 tablespoons at a time, allowing each addition to incorporate a bit before the next. When all the butter has been added turn the stand mixer back onto high and beat until the buttercream looks smooth. (It may look curdled and soupy at one point, but just keep beating).
Add elderflower liqueur and salt to the buttercream and beat to combine.
Place into a piping bag and pipe onto cooled cupcakes (I used Wilton 2D tip).