Preheat your oven to 350°F (175°C) and prepare a baking sheet with parchment paper for easy cookie removal later.

Cream together the light brown sugar and softened unsalted butter in a mixing bowl until the mixture is light and fluffy, about 2-3 minutes.

Add in the large egg and vanilla essence, mixing until everything is well-blended and the mixture looks smooth and silky.

Incorporate the all-purpose flour, baking powder, and salt gradually, mixing until a soft cookie dough forms.

Scoop tablespoon-sized amounts of the dough and place them on the prepared baking sheet, leaving some space between each cookie for expansion.

Bake in the preheated oven for approximately 12 minutes, or until the cookies are lightly golden at the edges.

Combine the cubed unsalted butter, white sugar, fresh lemon juice, lemon zest, egg yolks, and salt in a separate bowl to create the lemon curd. Whisk until smooth.

Cook the lemon curd mixture over low heat, stirring continuously, until it thickens and coats the back of a spoon. This should take around 8-10 minutes.

Beat the egg whites in another bowl until soft peaks form. Slowly add in the white sugar, salt, cornstarch, and vanilla essence, continuing to beat until stiff peaks form.

Spoon the thick lemon curd generously onto each baked cookie, then top with a dollop of meringue, spreading it to the edges.

Return the cookies to the oven for an additional 3-5 minutes or until the meringue is lightly browned and set.