For the Chocolate Macarons
Line a clean, flat cookie sheet with a Silpat, and set it aside.

Preheat oven to 325 degrees and place rack in middle of oven.

Sift together almond flour, cocoa powder, and confectioners' sugar, and set aside.

In a spotlessly clean stand mixer bowl, whip whites on medium speed until they are foamy and you can start to see the tines of the whip leaving a trail in the whites, about 1 to 2 minutes.

Add 1 tablespoon of sugar, and continue to whip for about 30 to 45 seconds. Add another tablespoon of sugar, and whip again for another 30 to 45 seconds. Repeat with the third and fourth tablespoons of sugar.

When all of the sugar is mixed in, whip the whites for about another minute or two until they become glossy and shiny. Remove from mixer.

Fold in about half of the almond flour/confectioners' sugar mix; when most of it is folded in, add the rest of the dry mix. Fold until mixture is smooth and a little stiff -- it should drop smoothly off of the spatula.

Using a piping bag and a small round tip, pipe out small rounds of macaron batter about 1 inch in diameter. Try to pipe straight down and quickly pull away when you are done to minimize peaks. Pipe until you’ve used up all the batter.

Rap the cookie sheet several times to flatten out the mounds and to pop any bubbles that might be in the batter.

Let cookies rest for about 15 to 30 minutes, until they are no longer tacky to the touch.

Place in oven, and immediately turn oven down to 300 degrees. After 8 minutes, rotate the cookie sheet. Depending upon your oven, cookies take from 15 to 20 minutes. Remove from oven, and let cool.

Remove the meringues from the parchment and pair them by size.

For the Espresso Buttercream
In a small metal or other heatproof bowl, whisk together the sugar and egg whites to make a thick slurry.

Place the bowl over (not touching) simmering water in a saucepan and heat, whisking occasionally, for 6 to 8 minutes, or until the mixture is hot to the touch. It will thin out a bit as the sugar melts.

Remove from the heat and scrape the mixture into the bowl of a stand mixer fitted with the whip attachment. Whip on medium-high speed for 6 to 8 minutes, or until the mixture becomes a light, white meringue and is cool to the touch.

Turn down the speed to low and add the chunks of butter one at a time. The mixture will look curdled at first, but don’t worry. Increase the mixer speed to medium and beat for about 3 to 4 minutes until the buttercream is smooth. Add the espresso and salt.

Buttercream may be used immediately or stored in an airtight container in the refrigerator for up to 4 days. Remove from fridge about 3 to 4 hours before using, and using the paddle attachment of the mixer, paddle the buttercream until it becomes smooth enough to use.

Fill the cookies
Using a piping bag with the same tip used to pipe the cookies, pipe 1 to 1-1/2 teaspoons of the filling onto half of the cookies—you want to use just enough filling that it spreads to the edge when topped but doesn’t squish out much when bitten. Top the filled halves with their partners. The cookies are best the day they’re made, but you can store them in an airtight container at room temperature for up to 1 day or in the freezer for up to 2 weeks.