In a mixing bowl, combine brown sugar, lemon zest, and softened butter. Beat until light and fluffy, about 3-4 minutes. Add one egg and vanilla extract, mixing until well-integrated.

Add flour, baking powder, and salt to the wet mixture. Fold dry ingredients until no flour streaks remain. Cover and chill in the refrigerator for 30 minutes.

Prepare the lemon curd by whisking sugar, lemon juice, lemon zest, egg yolks, and salt in a saucepan over medium heat. Stir until thickened, about 8-10 minutes. Sieve into a bowl, add butter, and mix until smooth. Chill until ready.

Preheat the oven to 350°F (175°C). Line baking sheets with parchment paper. Scoop tablespoon-sized dollops of dough onto prepared sheets, spacing 2 inches apart. Bake for 10-12 minutes until edges are light golden brown.

For the meringue, combine egg whites and sugar in a heat-proof bowl over simmering water. Heat to 170°F (76°C) while whisking until stiff peaks form, about 5-7 minutes.

Once cookies cool, top each with lemon curd. Pipe or spread meringue on top, creating a mountain shape.

Use a kitchen torch to toast the meringue until golden brown. Serve immediately or chill until ready to enjoy.