1. In a small bowl, whisk the brown sugar and yeast into the lukewarm water and let stand until foamy, about 5 minutes. In the bowl of a standing mixer fitted with the paddle, mix the flour with the salt and all of the spices.
2. Once the yeast is foamy, add the molasses to the yeast mixture and stir until thoroughly combined.
3. Make a well in the center of the flour and pour in the yeast mixture. Mix at medium speed until shaggy, about 1 minute. Add the eggs one at a time, mixing for 20 seconds between each. Whisk the vanilla with the melted butter. With the mixer at medium-low, gradually mix in the butter until smooth; the batter will be thick and very sticky.
4. Cover the bowl and let the batter rise in a warm place until doubled in size, about 1 hour and 45 minutes.
5. Stir the pearl sugar into the risen batter. Cover again and let rest for 15 minutes.
6. Preheat the oven to 250°. Preheat a Belgian waffle iron and brush it with melted butter (if your non-stick coating is in good shape you can skip this step).
7. Gently stir the waffle batter to deflate. Using about 1/4 cup of batter for each waffle, cook the waffles according to the manufacturer’s directions until they are golden and crisp (about 5 minutes); brushing the waffle iron with melted butter as needed.
8. Transfer the waffles to plates or keep them warm in the oven, then serve.

TO MAKE AHEAD:

1. The batter can be prepared without adding the pearl sugar and refrigerated overnight. Bring batter to room temperature the next day, stir in the pearl sugar and proceed with cooking the waffles.