- Build the Sandwiches:
- Spread butter over one side of each of the slices of bread. Flip the bread over so the buttered side is facing down as you build the sandwiches.
- Divide half of the shredded mozzarella between two slices of bread. Top the mozzarella with the crumbled feta.
- Divide the cooked spinach between the two sandwiches, then top with the remaining shredded mozzarella and a pinch of crushed red pepper flakes. Top each sandwich with the second slice of bread, buttered side facing out.
- Grill the Sandwiches:
- Heat a large skillet over medium-low. Once hot, add the sandwiches and cook on each side until golden brown and crispy on the outside and warm and gooey on the inside.
- Serve:
- Cut the sandwiches in half and serve!