Place the oreo shells in the bowl of a food processor and pulse on high speed until they are a fine crumb. Set aside until ready to use.

Place a small saucepan of water over medium-high heat and bring it to a gentle simmer. Add the egg whites and granulated sugar to a small heatproof bowl and set the bowl of the simmering water.

Whisk the egg whites and sugar together until the sugar has fully dissolved-- about 3-4 minutes.

Transfer the mixture to the bowl of a stand mixer fitted with the whisk attachment. Beat the egg whites on medium high speed for 3-4 minutes, or until they form stiff peaks.

Use a fine mesh sieve to sift the powdered sugar and almond flour into the egg whites. Gently fold the dry ingredients into the egg whites, making sure not to deflate the egg whites yet.

Once all of the dry ingredients have been incorporated (make sure to scrape all the way down to the bottom of the bowl), smush the batter against the sides of the bowl and fold it back together. Repeat the smush-and-fold process 4-5 times before testing the macarons for the lava stage.

The meringue is ready to pipe when it flows smoothly off the spatula. If it falls off in clumps, do a few more smush-and-folds before retesting. When the meringue flows smoothly, transfer it to a piping bag fitted with a round tip (I like a Wilton #10).

Pipe small (1.5”) macarons onto the sheet pans making sure to pipe them about 2” apart. Once you’ve finished piping the first tray, hold it about 6” off the counter and drop it straight down to release any air bubbles. Drop the tray 4-5 more times, or until it looks like any large air bubbles have popped. Repeat with the second tray.

Sprinkle about ¼ cup of oreo powder over the macarons and set them aside to rest for 25-30 minutes.

The macarons are ready to bake when they have developed a skin-- you should be able to touch them gently without the meringue sticking to your finger.

While the macarons rest, preheat your oven to 325F.

Bake the macarons, one tray at a time, for 14 minutes, turning the tray halfway through baking.

Allow the macarons to cool fully on the tray. Trying to remove the macarons while they are warm may result in sticking.

Add the softened butter to the bowl of a stand mixer fitted with the paddle attachment. Beat on high speed for 1 minute. Next, add the oreo fillings and vanilla extract and beat on medium-high speed until the mixture is combined and smooth. Make sure to scrape down the sides a few times so you don’t end up with clumps of butter.

With the mixer on low speed, slowly add the powdered sugar. If the mixture seems too dry, add 1-2 tablespoons of heavy cream (this isn’t always needed). Turn the mixer to high speed and whip the filling until the buttercream becomes light and fluffy-- about 2 minutes.

Next, fold in the remaining oreo crumbs and transfer the mixture to a piping bag fitted with your choice of tip.

Place the macarons in similar sized pairs and pipe a small dollop of filling onto one of the macarons. Add another macaron on top and press gently-- just until the filling reaches the edges. Repeat with the remaining macarons.

Transfer the macarons to an airtight container and store in the fridge to age overnight. Bring the macarons to room temperature before storing.