Step 1: Prepare the Macaron Shells

1. Sift Dry Ingredients: In a medium bowl, sift together almond flour, powdered sugar, and Oreo crumbs. Sifting removes any lumps and ensures a smooth macaron shell. Set aside.
2. Whip Egg Whites: In a clean, grease-free mixing bowl, add the egg whites. Use an electric mixer on medium speed to whip the whites until frothy, then add cream of tartar. Gradually add granulated sugar, one tablespoon at a time, and continue whipping until stiff, glossy peaks form. This process takes 5–7 minutes.
3. Add Vanilla: Gently fold in the vanilla extract, being careful not to deflate the meringue.
4. Combine Dry and Wet Ingredients: Add the sifted dry ingredients into the meringue in two additions. Use a spatula to fold the mixture gently, pressing out some air against the sides of the bowl. The batter is ready when it flows like “lava” and forms a ribbon that disappears back into the mixture after 10–15 seconds.
5. Pipe the Shells: Transfer the batter into a piping bag fitted with a round tip (such as Wilton #12). Pipe small, evenly sized circles (about 1.5 inches in diameter) onto a parchment-lined baking sheet. Tap the baking sheet firmly on the counter 2–3 times to release air bubbles. Use a toothpick to pop any remaining bubbles.
6. Rest the Shells: Let the piped macarons rest at room temperature for 30–45 minutes, or until a dry skin forms on the surface. You should be able to lightly touch the tops without them sticking to your finger.
7. Bake: Preheat your oven to 300°F (150°C). Bake the macarons on the center rack for 12–15 minutes. They’re done when the shells have developed “feet” (the ruffled edges at the bottom) and can be lifted off the parchment paper without sticking.
8. Cool: Allow the macarons to cool completely on the baking sheet before removing them.

Step 2: Make the Oreo Buttercream Filling

1. Beat Butter: In a large bowl, use an electric mixer to beat the softened butter until light and fluffy, about 2–3 minutes.
2. Add Powdered Sugar: Gradually add the powdered sugar and beat until combined.
3. Add Flavorings: Mix in Oreo crumbs, vanilla extract, and 1 tablespoon of heavy cream. Beat until smooth. If the frosting is too thick, add more cream, 1 teaspoon at a time, until desired consistency is achieved.

Step 3: Assemble the Macarons

1. Pair Shells: Match macaron shells of similar size into pairs.
2. Fill: Transfer the Oreo buttercream into a piping bag fitted with a small round tip. Pipe a small dollop of buttercream onto the flat side of one shell in each pair.
3. Sandwich: Gently press the second shell onto the filling, twisting slightly to spread the buttercream evenly to the edges.

Step 4: Mature the Macarons (Optional but Recommended)

1. Refrigerate Overnight: Place the assembled macarons in an airtight container and refrigerate for 24 hours. This allows the flavors to meld and the shells to soften slightly for a more cohesive texture.
2. Serve: Bring the macarons to room temperature before serving for the best flavor and texture.