In a large mixing bowl, cream together sugar, lemon zest, and softened butter until light and fluffy, about 3-4 minutes. Add in the beaten egg and vanilla extract, mixing until well combined. Gradually fold in the flour, baking powder, and salt, being careful not to overmix. Chill the dough in the refrigerator for 30 minutes to firm up.

In a medium saucepan, whisk together sugar, lemon juice, lemon zest, egg yolks, and a pinch of salt over medium heat. Stir consistently until the mixture thickens and reaches 170°F (76°C), about 8-10 minutes. Once thickened, strain the curd into a bowl and whisk in the cubed butter until smooth. Allow the mixture to cool, then refrigerate until set.

Preheat your oven to 350°F (175°C) and line baking sheets with parchment paper. Scoop chilled dough into small balls and arrange them on the prepared sheets, leaving space for spreading. Bake for 10-12 minutes or until the edges are lightly golden and the centers appear set. Let cookies cool completely on a wire rack.

In a heatproof bowl, combine egg whites and sugar. Place the bowl over a saucepan of simmering water, stirring gently until sugar dissolves and the mixture reaches 170°F (76°C). Remove from heat and whip with an electric mixer on high speed until stiff peaks form, about 5-7 minutes. The meringue should be glossy and hold its shape well.

Once the cookies are cooled, spread a teaspoon of chilled lemon curd on top of each cookie. Generously dollop meringue over the lemon curd, ensuring to cover it completely. Use a culinary torch to toast the meringue until golden brown, about 1-2 minutes, keeping the torch moving to avoid burning. Allow to cool slightly before serving, and enjoy your Best Lemon Meringue Pie Cookies!