Espresso Dark Chocolate Sandwich Cookies

Combine espresso powder with boiling water and stir to dissolve.

Using a stand mixer fitted with a paddle attachment, beat butter, sugar and confectioners sugar on medium-high speed for about 2 minutes. Add egg yolks, one at a time, and mix until well-combined. Add espresso mixture, vanilla, vanilla paste (if using) and salt and combine.

On low speed, mix in flour until just combined. Stop the mixer when you still see a few streaks of flour in the dough, then mix the rest by hand.

Transfer the dough to the counter and divide in half. Form each half into a disk, wrap each tightly in plastic wrap, and refrigerate for 2 hours.

Preheat oven to 325°F. Line 2 baking sheets with parchment paper. Remove one chilled dough disk from the fridge and let soften on the counter for about 10 minutes. Unwrap the dough and place it between 2 sheets of parchment paper. Roll out to a thickness about 1/4 inch.

Use a 2-inch cookie cutter to cut out cookies. Cut them as close together as possible. To prevent sticking, dip the edges of the cutter into some flour. Repeat with remaining disk. If the dough becomes too soft or warm, just pop it back in the fridge for a couple minutes.

Place the cookies on the prepared sheets about 2 inches apart. Bake for 12–15 minutes, until edges are slightly golden. Let cookies cool on sheets for 5 minutes, then transfer to wire rack.

To make the ganache, heat cream in a small saucepan over medium heat until simmering. Place chopped chocolate into a medium heat-safe bowl. Pour cream over the chocolate and let sit for 3–5 minutes. Add espresso powder and whisk chocolate and cream until smooth.

Refrigerate ganache, uncovered, stirring occasionally, until thickened, about 30–40 minutes.

Spread 2 teaspoons of ganache over half of the cookies, then top with remaining cookies, pressing lightly together. If ganache ever becomes too stiff, microwave on low for 10 seconds at a time, stirring in between each, until you get the desired consistency.