Warm the milk and mix with yeast and sugar; let sit until frothy.
In a large bowl, mix flour and salt, then add the yeast mixture, eggs, and vanilla.
Mix until a sticky dough forms, then gradually incorporate softened butter.
Knead the dough for 5–7 minutes until smooth, then cover and let rise for 1 hour.
Chill the dough in the refrigerator for at least 2 hours or overnight.
Fold in pearl sugar, divide dough into 8–10 balls.
Flatten each ball, add 1 teaspoon of Biscoff spread, and seal tightly.
Preheat a waffle iron and grease it lightly.
Cook each waffle for 3–4 minutes until golden and caramelized.
Serve warm with powdered sugar, berries, or extra Biscoff if desired.