Prepare Ganache: Finely chop the white chocolate and place it in a heatproof bowl. In a small saucepan, heat the heavy cream over medium until it just begins to simmer. Pour the hot cream over the chocolate, letting it sit for 1-2 minutes for melting, then whisk in the Biscoff spread until creamy. Allow the mixture to cool and firm up in the fridge for about 30 minutes.

Dry Ingredients: In a large bowl, sift together the almond flour, powdered sugar, and Biscoff cookie crumbs. Use a food processor if necessary to ensure this mixture is finely blended and free of lumps.

Meringue: In a clean mixing bowl, whisk the egg whites using a stand mixer or hand mixer on medium speed until foamy. Gradually add the granulated sugar while continuing to beat, increasing the speed to high. Whip the mixture until it reaches stiff peaks.

Macaronage: Gently fold the sifted dry ingredients into the meringue using a spatula. Be careful not to overmix; the macaron mixture should deflate slightly and become glossy.

Piping: Transfer the macaron batter into a piping bag fitted with a round tip. On a parchment-lined baking sheet, pipe uniform mounds, about 1.5 inches wide.

Resting: Let the piped macaron shells rest at room temperature for 30-60 minutes, or until a thin skin forms on top.

Baking: Preheat your oven to 145°C (290°F). Bake the macarons for about 14–15 minutes.

Assembly: Once the Biscoff macaron shells are cooled completely, pair them up by size and pipe or spread the creamy Biscoff ganache filling onto one shell.