The day before you make your cookies, make the lemon curd and refrigerate it so it’s nice and cold when you’re ready to assemble the cookies.
In the bowl of a stand mixer, beat the butter and sugar together until fluffy (about 3 minutes).
Add the lemon zest and the lemon oil or extract and mix for another minute or so. Lightly beat the egg and add it to the butter mixture, mixing for another minute. Be sure to scrape down the sides of the bowl.
Combine the flour, baking powder and salt in a separate bowl and then add it carefully to the butter mixture (with the speed on low), until it’s fully incorporated.
Gather the dough into a ball and cover with plastic wrap. Referigerate for an hour.
Just before you’re ready to bake your cookies, preheat the oven to 350 degrees F. and line two baking sheest with parchment paper.
Have your cookie cutter ready to go.
Roll out your cookie dough to a thickness of a 1/4 inch to just under 1/2 an inch (I like thicker cookies as they’re sturdier).
Use your cookie cutter to cut out as many cookies as you can, placing them on the prepared cookie sheets as you go.
Reroll the scraps and cut out more cookies until you’ve used all your dough.
Place the cookie trays in the freezer for 10 minutes to firm them up. Chilling the dough in this way will ensure that your cookies bake up smoothly and uniformly (and don’t spread out too much).
After having chilled the cookies, pop the trays in the oven for no more than 5 to 7 minutes (depending on your oven). You can rotate the trays as well to help ensure the cookies bake evenly. They should be just ever-so-slightly golden on the bottom. (This took about 6 minutes in my oven as my cookies were very small.)
Once baked, remove the cookies from the oven and make a small indentation in each one (you could use the end of a wooden spoon to do this). This will form a little valley in which to nestle your lemon curd.
Allow the cookies to cool completely on the trays before transferring the cookies to a wire rack.
Once completely cool, dollop a small amount of lemon curd in each of the valleys or indentations you made in the cookies.
To finish the cookies off, make the lemon meringue topping by placing your egg whites in the bowl of stand mixer with the whisk attachment.
Beat on high until soft peaks form and then gradually add in the sugar, beating on high.
After a few minutes the meringue will become stiff and glossy.
You can dollop the meringue on to the cookies or use a piping bag with a star tip.
If you want to go all out, get yourself a kitchen torch to brown the meringue a bit.
If you’re not serving the cookies right away, referigerate them. They will keep for two to three days.