Preheat a waffle iron. Whisk the flour, baking powder, baking soda and salt in a large bowl until combined. Whisk the sour cream, egg yolks, milk and vanilla in a medium bowl until smooth, then whisk in the melted butter and shortening.
Beat the egg whites in a separate large bowl with a mixer on medium-high speed until soft peaks form, about 3 minutes. Sprinkle in the brown sugar and continue beating until stiff glossy peaks form, about 4 more minutes.
Make a well in the center of the flour mixture, then gradually whisk in the sour cream mixture until just combined. Fold in the beaten egg whites until incorporated.
Brush the waffle iron with melted butter. Add 1/4 to 1/2 cup batter and cook according to the manufacturer's instructions. Repeat with the remaining batter, brushing the waffle iron with more butter between batches. Serve with syrup.
To keep pancakes and waffles warm, arrange on a rack set on a baking sheet and place in a 225 degrees F oven.