Beat unsalted butter and Speculoos cookie butter with an electric mixer until combined.

Add granulated sugar, brown sugar, baking soda, and baking powder. Beat until combined.

Beat in eggs and vanilla until combined.

Beat in as much flour as possible with the mixer, then stir in the remaining flour using a wooden spoon.

Cover and chill dough for about 1 hour or until easy to handle.

Preheat oven to 375 degrees F.

Shape dough into 1-inch balls and place on an ungreased cookie sheet.

Flatten balls with a fork or your hand, optionally dipping the fork in turbinado sugar.

Sprinkle the top with some turbinado sugar.

Bake for 7 to 9 minutes or until bottoms are light brown.

Transfer to a wire rack and let cool.

Combine Speculoos cookie butter, powdered sugar, and milk in a small bowl for the glaze.

Whisk until smooth, adjusting with more milk or powdered sugar as needed.

Drizzle glaze over cooled cookies.