Preheat oven to 350°F (175°C) and line baking sheets with parchment paper.

In a large bowl, cream together butter, Biscoff cookie butter, brown sugar, and granulated sugar until smooth and fluffy, about 2 minutes.

Mix in the egg, egg yolk, and vanilla until fully combined.

In a separate bowl, whisk together flour, baking soda, and salt.

Add dry ingredients to wet ingredients and mix until just combined.

Fold in white chocolate chips and crushed Biscoff cookies (if using).

Chill dough for 30 minutes for thicker cookies.

Scoop dough into 2-tablespoon balls and place 2–3 inches apart on baking sheets.

Bake for 10–12 minutes, until edges are set and centers look slightly underbaked.

Cool on the pan for 5 minutes, then transfer to a wire rack.