Preheat your oven to BROIL.
Melt the butter in a skillet over medium-high heat. Add the
garlic and cook until fragrant, about 30 seconds. Add the
artichoke hearts, Mozzarella cheese, Cheddar cheese, Parmesan
cheese and sour cream to the skillet and stir to blend. When
completely combined remove from the heat.
Slice the bread lengthwise. Spoon the artichoke mixture evenly
onto the bread. Broil for about 4-7 minutes or until cheese has
melted an bread is hot. Do not walk away. Watch the bread
closely or it could burn.