Preheat the oven to 350°F. Line a baking sheet with aluminum foil or parchment paper for easier cleanup.

Melt the butter in a small pan, and combine it with the garlic, salt, lemon juice, and parsley.

Halve the bread lengthwise and cut each half in half crosswise. Using your fingers, gently scoop out and discard some of the soft inner part of the thickest portion of the bread, leaving a 1-inch-thick shell. Brush the inside of the bread with the garlic butter. Place the sections, cut side up, on the prepared baking sheet, and bake in the oven until golden, aromatic, and lightly toasted, about 6 minutes. Remove the bread from the oven (leave it on the baking sheet) and raise the oven temperature to 400°F.

Heat the olive oil in a medium skillet over medium heat. Add the sausage and cook, stirring as needed, until it is browned and the fat is rendered, about 8 minutes. Using a slotted spoon, transfer the sausage to a paper-towel-lined plate, and set aside.

Spoon the tomato sauce evenly over the pieces of bread. Divide the mozzarella and Fontina evenly over the sauce. Top with the sausage, and then garnish with the thyme, crushed red pepper, and Parmesan. Bake for 8 minutes, or until hot and bubbly. Serve immediately, drizzled with extra-virgin olive oil if desired.