In a medium skillet over medium-high heat, cook the ground beef until completely browned, breaking it up with a wooden spoon for about 6 to 8 minutes. Drain any excess fat, then stir in the marinara sauce and simmer on low for 5 minutes until thickened.

In a small bowl, stir together the ricotta cheese, grated parmesan, and dried Italian seasoning until smooth and well combined.

In another small bowl, mix the softened butter and garlic powder together. Evenly spread the garlic butter on one side of each of the 8 sourdough bread slices.

To assemble, lay 4 slices of bread butter-side down on a clean work surface. Spread a quarter of the seasoned ricotta mixture on each slice, followed by a generous scoop of the warm meat sauce, and top with the shredded mozzarella.

Place the remaining 4 slices of bread on top, butter-side up, to close the sandwiches.

Heat a large non-stick skillet or griddle over medium heat. Place the sandwiches in the skillet and cook for 4 to 5 minutes per side, pressing down gently, until the bread is golden brown and the cheese is completely melted.

Cut the sandwiches diagonally and serve immediately while the cheese is hot and stretchy.