Preheat waffle iron. In a large mixing bowl, sift together flour, baking powder, sugar and baking soda. In a separate bowl, beat together egg yolks and milk. Add milk mixture, butter and oil to flour; stir gently to combine. Beat egg whites until stiff peaks have formed; fold into batter.
Spray preheated waffle iron with non-stick cooking spray. Pour mix onto hot waffle iron and sprinkle generously with chopped pecans. Cook until golden brown. Keep warm in oven while remaining waffles cook.