Lemon curd:

1. Whisk together sugar, lemon juice, zest and egg yolks.
2. Place over a pot of simmering water and cook, stirring occasionally, until thickened considerably (about 10 minutes).
3. Remove from heat and allow to cool for 10 minutes.
4. Add cubed butter, stirring until incorporated.
5. Pour into a jar or bowl, place a piece of plastic wrap onto the surface of the curd and refrigerate until chilled.

Lemon cupcakes:

1. In a bowl, massage the sugar and lemon zest together. Allow to sit for 5 minutes.
2. Whip the eggs and lemon sugar together until light and fluffy (about 2-3 minutes).
3. In one bowl, stir together the dry ingredients (flour, baking powder, baking soda and salt) and in another, whisk together the wet (vegetable oil, milk, sour cream and vanilla extract).
4. With the mixer on low, add half of the dry ingredients, mixing until just combined.
5. Add the wet ingredients, and continue mixing on low until just combined.
6. Repeat with the remaining dry ingredients.
7. Spoon four tablespoons of batter into each cavity of a lined cupcake pan.
8. Bake at 350F for 16-18 minutes, or until a toothpick inserted in the center comes out with only cooked crumbs.
9. Allow to cool in cupcake pan before moving to a cooling rack.

Filling the cupcakes:

1. Using a small pairing knife at a 45 degree angle, cut a cone shape piece of cake out of the center of each cupcake.
2. Cut the top off of each cone so only a thin layer remains.
3. Fill each cupcake with lemon curd.
4. Cover with the thin layer of cupcake you just cut.

Meringue frosting:

1. In the bowl of a stand mixer, whisk together the egg whites and sugar.
2. Place over a pot of boiling water and cook, stirring occasionally, until the sugar has dissolved and the mixture is hot (160F).
3. Return the bowl to the stand mixer and whip on high until light and fluffy.
4. Add the vanilla extract and whip on low until just combined.
5. Spoon the frosting into a piping bag with a large, round tip (like an Ateco 809), and pipe a low swirl, starting at the center of the cupcake and working outward.
6. Use an offset spatula to deepen the swirl or to create additional ridges to toast.
7. Use a chef's torch to toast the top of the meringue.