Begin by melting the white chocolate over a double boiler or in the microwave until smooth. Then, heat the heavy cream until just simmering, and pour it over the melted chocolate. Stir in the finely crushed Oreo cookies until blended. After mixing, let the ganache cool to room temperature, then refrigerate it for about 30-45 minutes until it firms up.

Sift together the almond flour, powdered sugar, and crushed Oreo cookies into a bowl. This step ensures that you have a fine, lump-free mixture for the macaron shells.

In a clean and dry mixing bowl, whisk the egg whites on medium speed until foamy. Gradually add the granulated sugar while whisking, and increase to high speed until stiff peaks form.

Gently fold the dry ingredients into the meringue using a spatula, being careful not to deflate it. The batter should flow smoothly like a ribbon when lifted.

Transfer the macaron batter into a piping bag fitted with a round tip. Pipe small rounds on a lined baking sheet, leaving space between them. Gently tap the baking sheet to release air bubbles.

Allow the piped macarons to rest at room temperature for about 45 minutes until a skin forms on the surface.

Preheat your oven to 145°C (290°F). Once dried, bake the macarons for 14-15 minutes until they detach easily from the parchment.

Pair up the macaron shells based on size and fill with the chilled Oreo ganache. Place a matching shell on top to create a sandwich.

Refrigerate the assembled macarons for at least 24 hours before serving for the best flavor and texture.