I got this recipe from a New Orleans food board in 1999. The person claimed that this was the recipe for the original spinach artichoke dip. I tried it and it seems like it was very close. Hope this helps!

SPINACH ARTICHOKE DIP - Copelands

1 stick (1/2 cup) butter
1/2 onion, chopped
2 boxes (10 oz. each) chopped spinach, cooked and drained
1 (8 oz.) package cream cheese, room temperature
1 cup sour cream
1/2 cup grated parmesan cheese
1 can artichoke hearts, drained and mashed
8 oz. Monterrey cheese, shredded
tortilla chips or fried bowtie pasta (for serving)

Melt butter add onion and saute until clear, about 5 minutes. Remove from heat and add remaining ingredients; blend well.

Microwave for 5 minutes.

Serve with tortilla chips or fried bowtie pasta.

Source: lorielyse, June 11, 1999