Hide the milk powder when you're feeding him normal meal.
Otherwise, he will rely on milk powder too much!
Set 20-30mins for every meal, if he cant finish then stop, let him know he needd to wait for next meal.
My son now only takes 8-20 mins to finish his meal, as he knows if he can't finish in time, he has to wait until the next meal.
This is a very good training to kids, parents have to be firm too!