Starting with the cookies: Preheat your oven to 350. Using a fork, cream together your butter and sugar until nice and creamy. Then, add in the egg yolk and vanilla extract, and mix again until creamy and well incorporated. Next, add in your dry ingredients and mix until the dough comes together and is holding its shape.
Using a large cookie scoop (3 tbsp), scoop out the cookies and place them on a parchment paper lined cookie sheet.
Place the cookies in the oven and bake for 13-14 min until JUST slightly starting to lightly brown. Remove and let cool.
Now, for the lemon curd. Add your lemon juice, egg yolks and sugar to a glass bowl.
Now, create a double boiler by bringing 1-2 inches of water to a simmer in a small saucepan and place the heatproof glass bowl on top, ensuring that it is not touching the water in the pan below it.
Whisk the ingredients on a continual basis as the lemon curd cooks. Continue to whisk the lemon curd for 10-15 minutes or until it begins to thicken. Once you remove it from the heat, if the curd stays parted for a second or 2 after running a spatula through it, that means it has cooked down properly. If the lemon curd isn’t thickening, turn up the heat a bit and continue to whisk.
Once you have removed the curd from the heat, add in your butter and whisk until the butter has melted and the curd has a creamy, silky texture. Allow the curd to cool completely. It should be a nice, thick, pudding-like consistency.
Lastly, we will make the meringue. Add the egg whites, sugar and cream of tartar to a heatproof bowl. Using the same double boiler, place the bowl over the saucepan filled with about two inches of simmering water.
Whisk the whites and sugar constantly until the mixture has thinned out and the sugar has dissolved completely. This should take about 4-5 minutes. To check if it is done, get a small amount of the mixture onto a spoon. Once it has cooled just slightly, dip your fingers into the mixture and rub it between your fingers. If you cannot feel any sugar granules, it is done cooking. If it still has even a slightly grainy texture, continue to heat the mixture.
Now, pour this mixture into a bowl on a stand mixer fitted with the whisk attachment. Beat the egg whites on medium low speed for 2-3 minutes and gradually increase the speed until the mixture reaches soft peaks and the bowl is no longer warm to the touch. Then increase the speed to high and beat until stiff peaks form. The meringue should be shiny, bright white, and hold its form well.
Now to assemble the cookies! Place the cooled curd into a piping bag fitted with a large circle piping tip. Add your meringue to another piping bag fitted with the piping tip of your choice. Add a dollop of the lemon curd to the center of the cookie. Next, pipe on a beautiful large swirl of the meringue directly on top of the curd, encircling the curd to help it stay in place.
Then, using a culinary torch, lightly toast the meringue topping. I find using small circular movements help achieve an even toast. Store in an air tight container in the refrigerator. Enjoy!