Measure butter and Biscoff spread into a microwave safe bowl. Heat in the microwave in 10 second bursts, stirring between each burst until you have a smooth liquid.
Add the milk and eggs and whisk together.
In a separate bowl, measure the flour and sugar.
Make a well in the flour mixture and pour some of the milk mixture into it.
Using your whisk, gradually incorporate flour into the liquid, adding more liquid as you go until it's all combined to a smooth batter.
Spoon a small ladleful of batter into the waffle maker. The batter will give 8 waffles in the Sage Smart Waffle Maker. Don't overfill your waffle iron as the batter with expand considerably as it cooks.
Cook for 3-5 minutes, depending on how well done you like your waffles.
Serve with Biscoff caramel sauce and some crumbled Lotus Biscoff cookies, if you like.