In a mixing bowl, combine flour, sugar, and yeast. Add eggs, warm milk, and vanilla extract. Mix until combined.
Add salt and softened butter. Knead dough for 8–10 minutes until smooth and elastic.
Cover dough and let it rise in a warm place for 1 to 1.5 hours until doubled in size.
Warm Biscoff spread slightly until it is soft and spreadable.
Punch down the dough and roll it into a 12×16 inch rectangle on a floured surface.
Spread the Biscoff evenly over the dough and sprinkle with crushed cookies.
Roll the dough tightly into a log, then slice it lengthwise and twist the halves together with filling side up.
Place the twisted dough in a greased loaf pan. Cover and let rise for another 30–45 minutes.
Preheat oven to 350°F (175°C).
Bake for 35–40 minutes until golden brown and a toothpick inserted in the center comes out clean.
While baking, combine sugar and water in a saucepan. Heat until sugar dissolves.
Once baked, brush the syrup over the warm babka for a glossy finish.