for the lemon slices
2-3 lemons, thinly sliced
3 cups water to blanch lemon slices
2 cup water
3 cups granulated sugar
for the cupcakes
1 3/4 cups all-purpose flour
1 1/2 teaspoons baking powder
3/4 teaspoons table salt
1 cup granulated sugar
1 1/2 sticks unsalted butter, softened but slightly cool, cut into 12 pieces
3 large eggs
3/4 cups milk
1 1/2 teaspoons vanilla extract
2 tablespoons finely chopped fresh rosemary
for the filling
4 large eggs
1 cup sugar
1/2 cup freshly squeezed lemon juice
4 tablespoons unsalted butter, softened to room temperature, cut into pieces
1/4 cup lemoncello
for the frosting
1 cup (2 sticks) unsalted butter, at room temperature
1/2 cup lemon curd (from the above)
3 cup confectioners sugar
First make the lemon slices. You will need a minimum of 24 hours for them to harden, so plan ahead (they can be made up to a week in advance). Thinly slice lemons. Blanch in 3 cups boiling water for 7 minutes; remove to an ice water bath. In the same saucepan, stir together 2 cups water and 3 cups sugar; stir to dissolve sugar. Add blanched lemon slices and heat until the mixture starts to boil slightly. Reduce to simmer; simmer uncovered for 1 to 1 1/2 hours, stirring occasionally and flipping the lemon slices over a few times. Remove from heat.
Spray a cooling rack with non-stick spray and place individual lemon slices in a single layer to dry for up to 24 hours (depends on how humid it is when you are making these). If making ahead of time, store in an airtight container separated with wax paper.
Make your lemon curd filling. In a medium saucepan, combine the eggs and sugar. Whisk together until well blended. Whisk in the lemon juice. Place the pan over medium-low heat. Cook, stirring or whisking constantly, until the mixture is warmed through. Be careful not to heat the mixture too quickly to avoid curdling the eggs. Whisk in the butter a little bit at a time, stirring in each addition until completely incorporated before adding more. Continue to cook, scraping the bottom of the pan, until the mixture thickens and a spoon or spatula leaves a path when drawn through it. Immediately remove the pan from the heat and pass the mixture through a fine mesh strainer. Transfer to an airtight container and refrigerate. (You can make this up to a week ahead of time.) Once the mixture is completely cooled, reserve 1/2 cup for the frosting, and add 1/3 cup lemoncello to the remainder.
For the cupcakes: Preheat oven to 350F. Line a muffin pan with paper baking cups and set aside.
In the bowl of a stand mixer, combine the flour, baking powder, salt, and sugar on low speed. Add the butter, 1 piece at a time, and combine until the mixture resembles coarse sand. Add the eggs, 1 at time, and mix until fully combined. Add the milk and vanilla, increase the speed to medium, and mix until the batter is light, fluffy and free of lumps.
Fill the lined muffin cups three-quarters full, being careful not to overfill. Bake until a toothpick inserted in the center of the cupcake comes out clean, about 12-15 minutes. Cool the cupcakes in the pan for 5 minutes, then transfer to a wire rack to cool completely.
To make the frosting, cream together the butter and lemon curd until light and fluffy. Mix in the confectioners sugar a little bit at a time. The frosting may be a little loose, so add a bit more powdered sugar as necessary. Refrigerate to set for 20-30 minutes while you fill the cupcakes.
To assemble the cupcakes, use the cone method to make a well in the center of each cupcake. Discard the cones. Fill each well with about 1 1/2 tablespoons of the lemoncello mixture and the replace the tops of the cupcake wells. Decorate with the frosting, place a candied lemon slice on each as well as a rosemary branch. Keep cool until serving.