Mix the Ricotta Filling – In a bowl, combine ricotta, Parmesan, salt, and pepper.
Assemble the Layers – Spread ricotta mix on 4 slices of bread. Top with spinach, sun-dried tomatoes, and mozzarella.
Top and Butter – Close each sandwich and butter the outsides generously.
Grill to Perfection – Toast on a skillet over medium heat for 3–4 minutes per side until golden and melty.
Let Rest & Serve – Rest 1 minute before slicing to avoid spills. Cut diagonally and serve warm.