Grilled Fontina and Eggplant Caviar Sandwich

Ingredients

• 2 large eggplants, 2 1/2 lbs total
• 2 tablespoons fresh lemon juice
• 2 cloves garlic, minced
• 1 teaspoon ground cumin
• 1/2 teaspoon sweet paprika
• 1/8 teaspoon cayenne pepper
• 1 tablespoon extra-virgin olive oil
• salt and freshly ground black pepper
• 2 tablespoons unsalted butter, at room temperature
• 12 slices coarse-textured white bread
• 6 oz. Fontina cheese, thinly sliced