Preheat the broiler to high.

Preheat a large skillet over medium heat.  Once hot, add the butter and allow to melt; add the onions and a pinch of salt, stirring to combine.  Sauté for 5 to 7 minutes, until softened and starting to turn a light golden color.  Add the garlic and red pepper flakes and cook for 30 seconds more, until fragrant.  Add the flour, stirring frequently, and cook for 3 minutes.  Slowly pour in the heavy cream; switch to a whisk and whisk until mixture is incorporated and lump-free.  Cook, stirring frequently, until the mixture thickens slightly, about 2 to 3 minutes.  Stir in the crème fraîche.

Reserve a small handful of each cheese to garnish the top.  Reduce the heat to medium-low and gradually begin adding the remaining cheeses, stirring to melt.  Continue until all of the cheese has been incorporated and the mixture is smooth.  Stir in the lemon juice and chopped artichokes.  If the mixture is too thick, you can add a little of the artichoke juice from the cans until it reaches your desired consistency.   If you reserved some whole quartered artichokes for the top, you can arrange them however you like to make them look pretty.  Cover the top with the reserved cheese and broil for 6 to 8 minutes, until the cheese is melted and golden-brown and the mixture is bubbly.  Garnish with fresh chives and serve with the toasted bread.