Make the vanilla cupcakes:

1. Combine the dry ingredients. Beat in the butter on medium low. The mixture should resemble coarse sand. Beat in the sugar on low.
2. Add the eggs one at a time, then the vanilla and milk. Mix until just combined.
3. Using an ice cream scoop or a spoon, pour into lined cupcake pan until 2/3 full.
4. Bake at 350 for 20 minutes or until a toothpick comes out clean. Let cool completely before frosting.

Make the lemon curd filling:

1. Heat lemon juice over medium heat until hot but not boiling.
2. Meanwhile, whisk eggs and yolk in a medium bowl. Gradually whisk in the sugar. While whisking, slowly pour hot lemon juice into the eggs. Return to saucepan and cook over medium heat. Stir constantly with a wooden spoon until mixture registers 170 degrees and coats the back of a spoon.
3. Remove pan from heat and stir in butter. Once melted, stir in cream, vanilla, and salt.
4. For a more even texture, strain mixture through a fine-mesh strainer (optional). Curd is able to be stored in an airtight container in the fridge for up to two weeks, just cover with plastic wrap to prevent it from drying out.

Make the lemon buttercream:

1. Bring a medium pot filled with one inch of simmering water to a boil. Place the egg whites and sugar in a stainless-steel bowl (like a stand mixer bowl) and place on saucepan. Use a whisk to beat the mixture until very hot (about 160F).
2. Remove from heat and mix with the whisk attachment on high until it is cool, thick and glossy and has tripled in volume, about 5 minutes.
3. Reduce speed to medium and add butter a few pieces at a time. Add the lemon zest and lemon juice and continue to beat until smooth and fluffy.*

Assemble the cupcakes:

1. Use an apple corer to gently hollow out the center of each cupcake, not going through the whole depth of the cupcake.
2. Spoon lemon curd into each cupcake. I like using an espresso spoon for this part!
3. Use an extra large closed star frosting tip to pipe a rosette on each cupcake. If you want, you can leave a space in the center and fill it with more lemon curd. Finish with a sprinkle of coarse sugar.