Mint Slices (Chocolate Cookies With Mint)

Yield:

12

Mint Slices are a rich chocolate cookie with a mint filling, sold in every Australian grocery store. Martha’s homemade version of the favorite calls for making thin, crisp dark chocolate cookies and sandwiching them with a fondant-like peppermint filling, then enrobing them in tempered chocolate. Making these indulgent treats is a project, but the cookie dough can be made up to two months ahead, and the finished cookies also freeze well—so set aside some time to make these much-loved treats from Down Under.

Directions

Prep baking sheets; combine dry ingredients for cookies:

Line two baking sheets with parchment. In a medium bowl, whisk together cocoa powder, flour, and salt; set aside.
Cream butter and sugar:

In the bowl of an electric mixer fitted with the paddle attachment, cream together butter and granulated sugar on medium speed until light and fluffy, about 3 minutes.
Add egg and vanilla:

Add egg and vanilla; beat until well incorporated, scraping down sides as necessary.
Add flour:

Reduce speed to low, add flour mixture, and mix until just combined; do not overmix.
Shape dough into disk and refrigerate:

Transfer dough to a piece of plastic wrap, shape into a disk, and wrap tightly. Refrigerate at least 1 hour.
Combine filling ingredients:

In the bowl of an electric mixer fitted with the paddle attachment, beat together confectioners' sugar, corn syrup, butter, and peppermint until well incorporated.
Shape filling into disk and refrigerate:

Transfer filling to a piece of plastic wrap, shape into a disk, and wrap tightly. Refrigerate at least 1 hour.
Preheat oven, roll dough and cut out cookies:

Preheat oven to 350°F. Roll out dough between two sheets of parchment to a 1/8-inch thickness. Using a 3-inch oval cookie cutter, cut out ovals and place 1 inch apart on prepared baking sheets.
Bake and cool cookies:

Bake until dry, 10 to 12 minutes. Let cool on sheets 5 minutes, then transfer to wire racks to cool completely.
Roll out and cut out filling; sandwich cookies:

Roll out filling between two sheets of parchment to a scant 1/4-inch thickness. Using the same cutter, cut out ovals and sandwich between two cookies.
Make chocolate coating:

Place 8 ounces chocolate in a metal (or other heatproof) bowl. Set bowl of chocolate over a saucepan containing 2 inches of water (don't let bottom touch the water). Heat over medium and bring to just below a simmer. Let melt, stirring gently until chocolate registers 115°F on thermometer. Remove bowl; add remaining 4 ounces chocolate to bowl, stirring constantly until chocolate registers 85°F. Return bowl to saucepan off the heat and stir constantly until chocolate registers 89°F. Use immediately, stirring frequently while using to maintain temper and prevent streaking once chocolate hardens.

If tempered chocolate thickens too much during use, place over simmering water again, stirring, 2 to 3 seconds.
Coat sandwich cookies in chocolate:

Working with one at a time, place each sandwich in tempered chocolate and turn to coat completely. Transfer to a fresh parchment-lined baking sheet. Working quickly with the back of the tines of a fork, gently tap top of each sandwich to create a design, then slide to another location on parchment to prevent a border from forming. Let stand until set, at least 30 minutes.