Preheat the oven to 350°F. Line a standard muffin tin with 12 paper cupcake liners. Set aside.

In a medium bowl, combine the all-purpose flour, baking powder, baking soda, and salt. Set aside.

In a large mixing bowl, cream together, using a handheld mixer on medium speed, the granulated sugar and unsalted butter until the butter is light and fluffy.

To the butter mixture, add the large egg, lemon extract, and vanilla extract, mixing until the egg is fully incorporated.

Add half the flour mixture, mixing just until incorporated, followed by the buttermilk and ending with the remaining flour mixture. Make sure to mix in each addition until fully incorporated. Your batter should be thick and smooth. Do not overmix your batter.

Allow the cupcakes to cool in the muffin pan for 5 minutes before transferring them to a cooling rack to cool completely.

Once your cupcakes have cooled completely, you can remove the centers of each cupcake with a cupcake corer or serrated spoon and spoon in about 1-1½ tablespoons of prepared lemon curd into the centers of the cupcake. Be very careful not to remove too much of the center, as you still need your cupcake to have some stability when frosted with the meringue.

After your cupcakes have cooled and been filled with lemon curd, you can make your meringue by adding, to a very clean stainless steel bowl of a stand mixer, the egg whites and cream of tartar. Whip on high speed, using the whisk attachment, until the egg whites become very frothy and soft peaks start to form.

While the mixer is running at medium speed, slowly add the superfine granulated sugar. Continue to whip until the meringue is light, fluffy, and stiff peaks form.

You can either mound the meringue onto the tops of each filled cupcake, or you can pipe it on using a large piping bag fitted with a large piping tip.

Being very careful, you can use a small kitchen torch to lightly toast the meringue on each cupcake.