Preheat your oven to 350°F. In a large bowl, cream together the softened butter and 1.75 cups granulated sugar until light and fluffy, about 2-3 minutes. Add the egg, egg yolk, lemon essence, and vanilla extract, mixing until fully combined. In a separate bowl, whisk together the baking powder, baking soda, salt, and all-purpose flour. Add the dry ingredient mixture to the wet ingredients and stir until just combined into a cohesive dough. I like to use room-temperature butter for creaming—it incorporates air more easily and gives you fluffier cookies.

Roll the dough into 1-tablespoon-sized balls and place them on a baking sheet, spacing them about 1 inch apart. Bake at 350°F for 8 minutes, until the edges are just set but the centers remain slightly soft—they should not be fully baked since they'll firm up as they cool and later receive the hot lemon filling. Remove from the oven and allow the cookies to cool completely on the baking sheet before handling.

While the cookies cool, whisk the 5 large egg yolks in a bowl and set aside. In a medium saucepan, combine the lemon zest, lemon juice, water, cornstarch, 0.75 cup granulated sugar, and 0.5 tsp salt. Cook over medium heat, stirring frequently, until the mixture simmers and thickens slightly, about 3-5 minutes. Slowly pour about half of the hot lemon mixture into the whisked egg yolks while stirring constantly to temper them and prevent scrambling. Return this mixture to the saucepan with the remaining lemon filling and cook, stirring continuously, for another 1-3 minutes until the curd is thick enough to coat the back of a spoon. Remove from heat and let cool for a few minutes before using. I find that tempering the yolks gradually prevents lumps and gives you the silkiest curd.

In a heatproof bowl, combine the 5 large egg whites (at room temperature), 0.5 tsp cream of tartar, 0.6 cup granulated sugar, and a pinch of salt. Set the bowl over a pot of simmering water (making sure the bottom doesn't touch the water) and whisk constantly until the mixture is warm to the touch and the sugar has fully dissolved, about 3-5 minutes. Transfer the mixture to a mixer and beat on medium-high speed until stiff, glossy peaks form—this creates a stable meringue that won't weep. Room-temperature egg whites whip to greater volume than cold ones, so plan ahead if you have time to let them sit out.

Spoon or pipe about 1 teaspoon of the lemon curd filling from Step 3 onto the center of each cooled cookie. Top each with a generous dollop of the meringue from Step 4, using the back of a spoon to create decorative peaks. Using a kitchen torch, carefully brown the meringue peaks until they turn golden-brown and slightly caramelized, rotating each cookie as needed to ensure even browning. Work quickly and don't hold the torch in one spot too long to avoid burning the meringue.