Cook bacon in a medium skillet over medium heat until crisp; remove with a slotted spoon to a paper towel to drain.
Discard all but 1 tablespoon of the bacon fat remaining in the skillet. Add 4 tablespoons butter and melt. Add the onion, garlic, salt, black pepper and crushed red pepper. Cook, stirring as needed, until the onion is very soft, about 10 minutes. Add the artichokes and cook for 2 minutes longer. Add 1 bag of spinach and cook until wilted, about 2 minutes; then add the second bag and cook, stirring as needed, for 4 minutes until the spinach is tender and the flavors have blended. Remove from the heat.
Set a strainer over a bowl and add the spinach-artichoke mixture. Allow the excess liquid to drain, about 5 minutes.