Preheat broiler, and line a baking sheet with foil.
In a large skillet over medium-high heat, melt butter until foamy. Add garlic and cook until fragrant, about 30 seconds.
Remove from heat and stir in artichoke hearts, mozzarella, cheddar, parmesan, sour cream and shallot until combined.
Slice the bread lengthwise. Place the bread halves on prepared baking sheet, cut side up, and spoon the cooled cheese and artichoke spread over the top of each half.