Sift the cornstarch, flour, baking powder, baking soda, and salt together in a bowl. Whisk to combine and set aside.
Place the butter and sugar in the mixing bowl of a stand mixer fitted with a paddle attachment. Cream the butter and sugar together until light and fluffy.
Add the egg yolks to the butter and sugar mixture one at a time, pausing between each addition. Add the vanilla and beat until no longer visible. Pour in the flour mixture and beat until a crumbly dough forms. Add the cream and beat until dough becomes silky.
Transfer the dough to the counter and form into a disc. Wrap the dough in plastic wrap and place in the fridge. Let chill for 1 hour.
Once an hour has passed, place the dough on a well-floured surface. Roll the dough out until it is a ¼ of an inch thick. Punch cookies out of the dough using a 1 ½" round cookie cutter. Transfer the cookies to a baking sheet lined with parchment paper or a silicone mat and place them the oven. Bake the cookies for 15-20 minutes or until golden.
Transfer the cookies to a wire rack and let cool completely.
For the Ganache
Place the chocolate chips in a medium-sized bowl and set aside.
Pour the dulce de leche and cream into a saucepan and place over medium-low heat. Heat until the mixture is hot like bath water but don't let it come to a boil.
Pour the hot dulce de leche mixture over the chocolate chips and let sit for 1 minute. Once the minute has passed, whisk until a smooth and glossy mixture forms. Add the salt and stir to combine. Cover the ganache and let sit at room temperature for at least 30 minutes.
For the Meringue
Place the egg whites in the bowl of a stand mixer fitted with a whisk attachment. Add the cream of tartar and whisk the egg whites on high until foamy.
While the egg whites are being whisked, pour the sugar and water into a small saucepan and place over high heat. Heat the mixture until it reaches 240°F.
With the mixer mixing on medium-high, slowly pour the hot sugar mixture into the egg whites. Continue whisking until stiff peaks form.
Transfer the finished meringue to a piping bag fitting with a large piping tip - I used a Wilton 6B.
To Assemble
Spread roughly a teaspoon of the ganache on half of the cookies. Pipe a dollop of the meringue on top of the ganache and toast with a kitchen torch. Place the remaining cookies on top and gently press. Serve the S'more Alfajores immediately.
Notes
**I used Eagle brand dulce de leche, which has a very runny consistency. If yours does not thin it out with additional cream.
Keyword chocolate, cookies, dulce de leche, ganache, meringue, s'mores