Heat milk in small saucepan until lukewarm, 110 to 116°F on an instant-read thermometer. Transfer the milk to the bowl of a stand mixer and add brown sugar and yeast and stir to combine. Let sit for 5 minutes or until yeast begins to form.
Add the eggs, melted butter and vanilla extract and mix with dough hook until combined.
Add 2 ⅔ cups flour and salt and mix on low speed until dough is smooth. Add remaining cup of flour and mix on low for 5 minutes, or until glossy and dough is pulling away from side of bowl.
Cover bowl with plastic wrap and place in warm place for 30 minutes.
Use your hands or a spoon to fold in the pearl sugar. Divide the dough into 10-12 balls.
Heat your waffle iron according to the manufacturer’s instructions. Working with 1 ball of dough at a time, arrange on the waffle iron and cook until golden brown all over, 2 to 5 minutes depending on your iron. Repeat with remaining dough.
Notes
If you use instant yeast, you don't have to wait for it to sit in the milk for 5 minutes.
If the dough isn't pulling away from the bowl after adding the flour, add 1 tablespoon of flour at a time until it does.
Avoid opening the waffle iron too soon. It's tempting to peek at the waffles as they cook, but avoid opening the waffle iron too early. Opening it prematurely can cause the waffle to tear or stick to the iron, resulting in an unevenly cooked waffle.
Keep the waffles in a 200°F oven while making the others to keep warm.
Clean your waffle iron while it is still warm with a damp cloth or paper towel.