Place popped popping corn in a large roasting pan.

In a heavy saucepan stir together sugars,, butter, corn syrup and cream of tartar.

Bring to boil and boil for 5 minutes without stirring.

Remove from heat, add baking soda and stir well.

Pour sugar mixture over popcorn and mix to coat well.

Bake in 200°F. oven for one hour, stirring every 10 minutes.

Let cool, stirring occasionally.

Store in airtight container.

Makes 20 cups, and disappears quickly!