Preheat a waffle iron according to the manufacturer’s instructions. Spray it with nonstick cooking spray.
In a large mixing bowl, sift together flour, baking powder, salt, cinnamon and nutmeg, then whisk in the sugar.
In a separate medium bowl, whisk together milk, yogurt, eggs, maple syrup and vanilla until smooth.
Add the wet ingredients to the dry ingredients, folding with a rubber spatula until no streaks of flour remain. Whisk in melted butter.
Ladle in enough waffle batter to fill the waffle iron almost to the edges (about heaping ¼ cup), and close the iron. Cook until the waffles are golden brown and crisp, 6-8 minutes, then remove the waffles to a plate and repeat with remaining batter. Makes 12-15 waffles.
In a small bowl, whisk together the butter, sugar and cinnamon. Dollop on top of the hot waffles and top with fresh fruit, if desired.