1 1/2 tablespoons light brown sugar
1 3/4 teaspoons active dry yeast
1/3 cup lukewarm water
2 cups all-purpose flour
1/2 teaspoon salt
3 large eggs
1 teaspoon pure vanilla extract
2 sticks unsalted butter, melted (about 1 cup), plus more for brushing
1 cup Belgian pearl sugar (see Note)
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. Make a well in the center of the bowl 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 1 cup of melted butter. With the mixer at medium-low, gradually mix in the butter until smooth; the batter will be thick and very sticky. Cover the bowl with plastic wrap and let the batter rise in a warm place until doubled in size, about 1 hour and 45 minutes.
Stir the pearl sugar into the risen batter. Cover again and let rest for 15 minutes.
Preheat the oven to 250°. Preheat a Belgian waffle iron and brush it with melted butter. Gently stir the batter to deflate. Using about 2 tablespoons of batter for each, cook the waffles according to the manufacture's directions until they are golden and crisp; brush the waffle iron with melted butter as needed. Transfer the waffles to plates or keep them warm in the oven, then serve.
MAKE AHEAD
The batter can be prepared through Step 1 and refrigerated overnight.

NOTES
Belgian pearl sugar is available at specialty shops and at amazon.com.