Preheat your oven to 350°F. Line a standard muffin tin with 12 paper cupcake liners to prepare for the cupcake batter. This will ensure they don’t stick and are easy to remove after baking.
In a medium bowl, combine 1¾ cups all-purpose flour, ¾ teaspoon baking powder, ¼ teaspoon baking soda, and ½ teaspoon salt. Mix the dry ingredients together until well combined, then set the bowl aside. This blend will create the structure of your cupcakes.
In a large mixing bowl, cream together ¾ cup granulated sugar and 6 tablespoons unsalted butter using a handheld mixer on medium speed. Keep whipping until the mixture is light and fluffy, which usually takes about 3 to 5 minutes. This step is crucial for achieving the right texture in your cupcakes.
To the fluffy butter-sugar mix, add 1 large egg, 1 teaspoon lemon extract, and ½ teaspoon vanilla extract. Mix well until all ingredients are incorporated and the mixture appears smooth.
Now it’s time to add your dry ingredients. Start with half of the flour mixture you set aside, mixing just until incorporated. Follow this with ¾ cup buttermilk and then the remaining flour mixture. Stir until all the ingredients are just combined; your batter should be thick and smooth. Be careful not to overmix, as this can make your cupcakes dense.
Fill each cupcake liner about two-thirds full with the batter. This will allow enough space for them to rise without spilling over. Use a spoon or a scoop for even distribution.
Place the muffin tin in the preheated oven and bake for 22 to 25 minutes. To check for doneness, insert a toothpick into the center of a cupcake; if it comes out clean, they’re ready!
Once baked, allow the cupcakes to cool in the muffin pan for 5 minutes. After that, transfer them to a cooling rack to cool completely. This ensures they set correctly and won't crumble when filled.
After your cupcakes have completely cooled, carefully remove the centers of each with a cupcake corer or a serrated spoon. Spoon in about 1 to 1½ tablespoons of prepared lemon curd into the centers. Ensure you leave enough structure for the meringue to sit on top.
Now, let’s whip up the meringue! In a clean stainless steel bowl of a stand mixer, add ½ cup egg whites and ¼ teaspoon cream of tartar. Start whipping on high speed using the whisk attachment. Watch as the egg whites become frothy and soft peaks begin to form.
While the mixer is running, slowly add ¼ cup superfine granulated sugar. Keep whipping until the meringue is light, fluffy, and stiff peaks form. This indicates your meringue is ready to be piped or spread onto the cupcakes.
With great care, mound or pipe the meringue onto the tops of each filled cupcake. Use a large piping bag fitted with a wide tip for a professional look.
For the finishing touch, use a small kitchen torch to lightly toast the meringue on each cupcake. This adds a lovely color and a toasted flavor that complements the lemon beautifully.