Set eggs and butter out to come to room temperature.

Preheat oven to 350 degrees. Line baking sheets with parchment paper.

In a medium bowl, whisk together the flour, cocoa powder, cornstarch, milk powder, baking powder, baking soda and salt until well combined; set aside.

In a large bowl using a hand-held mixer or stand mixer fitted with a paddle attachment, beat the butter, both sugars and espresso powder on medium speed until completely creamy and fluffy (about 3-4 minutes).

Scrape down the sides and add in the eggs one at a time, beating well between until each is fully mixed in.

Add corn syrup and vanilla extract; beat until well blended.

Scrape down the sides and add in the flour mixture, ½ at a time, mixing just until blended.

Using a large cookie scoop (3 Tablespoon size), scoop out cookie dough and roll into a ball with your hands.

Place six cookie dough balls on each baking sheet, leaving room between each cookie as the cookies will spread when they bake.

Flatten the cookie dough balls by pressing gently with your hand to about ¾-inch thickness.

Bake for 12-14 minutes or until the centers of the cookies have puffed up and are no longer glossy.

Remove from oven and allow cookies to cool on the baking sheets.

Prepare Marshmallow Meringue Frosting: Fill a double boiler with 1-2 inches of water and heat to a simmer. In a double boiler insert, stir together the granulated sugar and egg whites.

Place the insert over the simmering water, and whisk constantly until the sugar is dissolved and the mixture reaches 160 degrees.

Pour the hot mixture into the bowl of a stand mixer that has been fitted with a whisk attachment. Beat on medium speed until stiff peaks form, about 4-5 minutes.

Add the marshmallow crème and pure vanilla extract. Beat on high speed until stiff peaks form (another 4-5 minutes).

Spoon Marshmallow Meringue Frosting into a large piping bag fitted with a large round tip. Pipe the frosting onto cookies.

Prepare Chocolate Ganache: In a microwave-safe bowl, add the chocolate chips and the heavy cream and microwave at 50% power in 30-second intervals until melted and smooth.

Spoon 2 tablespoons of the warm Chocolate Ganache over each cookie.

Prepare White Chocolate Swirl: Place the chopped white chocolate in a microwave-safe bowl and microwave at 50% power in 30-second intervals until melted and smooth.

Pipe the signature Hostess loopy white circles across the center of each cookie.

Chill cookies until ready to serve.