Preheat the oven to 400°F (200°C).
Heat the olive oil in a skillet over medium-low heat. Add the garlic and cook for 30 seconds. Add the spinach and cook until wilted, about 5-6 minutes.
In a bowl, mix together the cream cheese, sour cream, artichoke hearts, half of the cheddar cheese, and all of the parmesan. Season with salt and pepper. Stir in the cooked spinach mixture until well combined.
Line a baking sheet with parchment paper. Slice a grid pattern into the loaf of bread, leaving about an inch uncut at the bottom.
Gently pry apart the bread squares. Drizzle or brush 3 tablespoons of melted butter into the crevices and on top.
Stuff the spinach artichoke mixture into the crevices of the bread, using a knife if needed. Pack as much as possible into each slice.
Sprinkle the remaining cheddar cheese over the top. Drizzle the remaining melted butter all over the bread.
Bake for 15-20 minutes, until golden, cheesy, and toasty. Sprinkle with fresh parsley before serving.