Actually post workout you want quick digesting carbs so the only solid food that would work would be sweets or sugary breakfast cereals. So dextrose is the most convenient thing to have as soon as you've finished training and then follow that with a solid meal within an hour.
That's what you want post workout, Whey and Glucose to feed those depleted muscles quickly. Just make sure your smoothy doesn't have fat in it. That slows down digestion and you don't want that.
