Isler Cookies

In a large bowl, combine flour, powdered sugar, and salt. Add the cold, diced butter and rub it into the flour mixture until it resembles coarse crumbs. Stir in the egg yolk, vanilla extract, and lemon zest, then quickly knead into a smooth dough. Wrap in plastic film and refrigerate for at least 30 minutes.

Preheat your oven to 180°C (350°F) and line a baking sheet with parchment paper. On a lightly floured surface, roll out the dough to about 3 mm thickness, then cut out circles with a 4-5 cm diameter cutter. Place the circles on the baking sheet and bake for 10-12 minutes, or until the edges are lightly golden. Let them cool completely on a wire rack.

While the cookies cool, prepare the buttercream: in a bowl, cream together the room temperature butter with powdered sugar, milk, and vanilla extract until light and fluffy. Spread a thin layer of raspberry jam on half of the cooled cookies, and buttercream on the other half. Sandwich one jam-covered cookie with one buttercream-covered cookie.

Melt the dark chocolate with coconut oil over a double boiler or in the microwave until smooth and glossy. Dip the top of each assembled Isler cookie into the chocolate glaze, then place them on parchment paper to set. Let them sit at room temperature or refrigerate for 30-60 minutes until the chocolate is completely firm.