Liège waffles are made with a dough similar to brioche, and the final product is waffles that are rich and perfectly sweet from the use of Belgian pearl sugar.
Place 1/2 cup warm milk in the bowl of a stand mixer (or large bowl if mixing by hand). Sprinkle with 1 packet instant dry yeast and 2 tablespoons packed light brown sugar, and stir to combine. Set aside until the yeast begins to foam, 4 to 5 minutes. Meanwhile, melt 1 1/2 sticks unsalted butter over low heat or in the microwave, about 50 seconds.
Add the melted butter and 3 large eggs to the bowl and whisk together until fully combined. Add 2 1/2 cups all-purpose flour, 1 teaspoon vanilla extract, and 1/2 teaspoon kosher salt. Mix with the dough hook (or wooden spoon) on low speed until completely smooth, about 2 minutes. Cover the bowl with a kitchen towel and let the dough rise at room temperature until it relaxes, about 30 minutes.
Add 1 cup pearl sugar and fold into the dough with a large spoon. Cover the bowl again and let the dough rise for 10 minutes more. Meanwhile, heat a Belgian waffle iron over medium heat.
Coat the waffle iron with cooking spray and scoop 1/4 cup of the batter into the center. Cook until golden-brown, typically 4 to 6 minutes.
Transfer the waffle with tongs to a wire rack. Repeat cooking the remaining batter, coating the iron with cooking spray between each. Enjoy while still warm, or keep warm in a 275ºF oven.
