Preheat the oven to 375°F. Line a baking sheet with parchment and set aside.
Cream together the butter and sugar until light and fluffy. Add in the egg yolk and vanilla extract. Mix in the flour and cornstarch.
Separate the dough into 10 equal sized balls and place on prepared baking sheet. Using a large spoon or small measuring cup create an indentation in the middle of the cookie dough ball.
Use your hands to form a bigger indentation in the middle and make sure to press the sides up a bit, this will hold the curd after baking.
Bake the cookies for 12-15 minutes until slightly golden brown.
While the cookies are still warm, use a spoon to press the indentation back in case it lost its shape any during baking.
Once the cookies are cool, spoon some lemon curd into each cookie. Set aside.
To make the meringue: add the sugar and egg whites in a double boiler over simmering water. Whisk the egg whites and sugar together constantly until the mixture reaches 160°F. Carefully pour the mixture into the bowl of your stand mixture and using the whisk attachment whip until stiff glossy peaks form.
Once stiff peaks form, transfer the meringue to a piping bag. (Or ziploc bag with the corner snipped off.)
Pipe the meringue onto the cookies. Using a kitchen torch, carefully brown the meringue. Enjoy!
Notes
How to Make Lemon Curd:Add 1 ½ cups sugar, zest from 1 lemon, ½ cup lemon juice and 4 egg yolks to a medium sized saucepan. Whisk over medium heat until completely combined. Whisk constantly until the curd reaches 170°F and has thickened up. Slice up ½ cup butter. Remove pan from the heat and stir in the butter until all melted and combined. Curd will thicken as it cools. Store leftovers in an airtight container in the refrigerator for up to 3 days.