Preheat Oven & Prepare Pan: Preheat the oven to 375°F (190°C). Line a rimmed baking sheet with parchment paper.
Mix the Filling: In a medium mixing bowl, combine the softened cream cheese, sour cream, ½ cup Parmesan cheese, garlic powder, nutmeg, salt, and cayenne pepper. Stir until smooth and fully incorporated. Fold in the drained spinach, chopped artichoke hearts, and 1 cup of the shredded mozzarella cheese. Mix until evenly distributed.
Assemble the Sliders: Using a serrated knife, carefully slice the entire sheet of slider buns horizontally through the middle, keeping the top and bottom halves connected. Place the bottom half of the buns on the prepared baking sheet. Spread the spinach-artichoke mixture evenly over the bottom layer. Sprinkle the remaining ½ cup of mozzarella cheese across the filling. Gently place the top half of the buns over the cheese layer.
Apply the Buttery Topping: In a small bowl, whisk together the melted butter and 2 tablespoons of grated Parmesan cheese. Using a pastry brush, generously coat the tops of the slider buns with the butter mixture, ensuring full coverage.
Bake: Cover the assembled sliders loosely with aluminum foil. Bake for 20 minutes. Remove the foil and continue baking for an additional 5 minutes, or until the cheese is bubbly and the tops are golden.
Serve: Allow the sliders to cool for 2–3 minutes before slicing into individual portions. Serve warm.