Melt butter in a large saucepan over medium heat. Stir in the spinach. Cook until tender.. about 10 minutes. Mix cream cheese and sour cream into the spinach mixture. When the cream cheese and sour cream are blended in,stir in Parmesan cheese and garlic salt.
Cook,stirring occasionally until thickened. About 10 minutes. Serve Warm. You can also transfer to a crock pot and put on the LOWEST setting if you are having a party. If you don't put it on the lowest setting,it may burn a bit.