For The Cookies:

In a stand mixer fitted with the paddle attachment, beat the butter, sugars, and salt together on medium speed until well combined. Add the egg, egg yolk, vanilla and lemon zest and mix until combined.

In a separate bowl, whisk the flour and cornstarch together. Add the dry ingredients to the wet ingredients in the mixer and combine until a dough ball is formed. Shape the dough into a flat disk, cover with plastic wrap and refrigerate for 1 hour.

Preheat the oven to 325°F and line a large baking sheet with parchment paper.

Once the dough is chilled, roll it out on a large piece of parchment paper to 1/8" thickness. For palm sized Moon Pies, use a large cookie cutter or the outer ring from a wide mouthed canning jar to cut round shapes out of the dough. Place the rounds 1" apart on the prepared baking sheet and bake for 8-10 minutes, until the edges of the cookies are lightly browned.

Let the cookies cool on the baking sheet for 5 minutes, then transfer to a rack to cool completely.

For The Filling:

In a small bowl, sprinkle the gelatin over the 1-1/2 tablespoons of water and set aside to bloom.

Combine the sugar, corn syrup and 2 tablespoons of water in a small saucepan. Bring mixture to a boil and cook until the mixture reaches 235°F.

Once the syrup reaches 235°F, add in the softened gelatin and mix until fully dissolved. 

Meanwhile, in a stand mixer using the whisk attachment, beat the egg white on medium speed until soft peaks form. With the mixer running on low, slowly pour the syrup mixture into the beaten egg white.

Turn the mixer to high speed and continue to beat until stiff. This will take 5-6 minutes. Watch the strands of fluff around the whisk. As the fluff becomes stiffer, these strands thicken up. In the last 30 seconds of beating the marshmallow fluff, slowly sprinkle in the ground Irish Breakfast.

The marshmallow fluff may turn out thicker or thinner depending on the humidity in your area. If it is nice and stiff, use an oiled rubber spatula to scoop out a generous portion onto each one of half the cookies.

If it is thinner, transfer the marshmallow fluff into a pastry bag with a round tip. Pipe a large round of marshmallow on the bottom side of half the cookies. Top the fluffed round with a second cookie to form a sandwich. Refrigerate for 30 minutes. This is important so the cookies stay together as they get dipped in the warm chocolate.

For The Chocolate Glaze:

Add about an inch of water to a sauce pan and place a heat resistant bowl on top. Select a bowl that is wide enough to dip your Moon Pies in, with sides that are not too high. This will make the chocolate dipping easier. 

Add the chocolate and oil to the bowl. Heat water on low, stirring the chocolate constantly until the chocolate is completely melted, which should take about 5 minutes.

Remove the bowl from the heat once the chocolate is melted to prevent burning. Working with one cookie sandwich at a time, use small tongs dip the cookie into the bowl of melted chocolate.

Flip it over to fully coat the cookie in chocolate. Tap off any excess chocolate back into the bowl. Place the cookies on a wire rack set over a large baking sheet. Refrigerate until chocolate is set.

Keep cookies stored in the refrigerator until ready to serve. They keep well for up to a week.