Finely chop the white chocolate and place in a heatproof bowl. Heat the heavy cream until simmering, pour over the chocolate, let sit for a minute, then mix until smooth. Stir in crushed Oreo crumbs and cool for 30 minutes.

Sift together the almond flour, powdered sugar, and Oreo cookie crumbs into a mixing bowl. Fluff with a spatula, sift again, and set aside.

In a clean bowl, beat egg whites on medium speed until foamy. Gradually add granulated sugar, then increase speed to high and whisk to stiff peaks (5-7 minutes).

Gently fold dry ingredients into meringue using a spatula until smooth and flowing in ribbons.

Transfer batter to a piping bag and pipe small mounds on a lined baking sheet, spacing them evenly. Let rest at room temperature for 45 minutes.

Preheat oven to 300°F (150°C). Bake macarons for 14-15 minutes until they form a dome and lift from the parchment.

Once cooled, peel macarons off the parchment. Pipe ganache onto one shell and sandwich with another. Repeat with remaining shells.