The night before, soak your beans in a covered bowl of water. In the morning, drain and rinse the beans. Place in a slow cooker with water, salt, bay leaves, and rosemary sprig. Cook on low for 8 hours. Do not pick up the lid.
Putting it all together: Fire up your grill on medium heat. Using a paring knife, remove peel from the eggplant. Slice into 1/2 pieces. Lightly brush with olive oil and sprinkle lightly with salt.
Remove loose skin from garlic. Cut the top 1/4 inch off of the head of garlic.
Lightly drizzle the exposed garlic cloves with oil. Place on grill.
Cut the dark green leaves off the leek, discard. Slice the remaining white and light green stalk in half lengthwise. Brush lightly with oil. Place leek cut side down on the grill.
Place eggplant on grill and press lightly. Cook 5-6 minutes on each side (leave the leek face down).
I like to close the grill lid to let the smoke work its magic. Be careful not to let them burn.
Remove from grill. Set eggplant aside. Carefully chop leek into small pieces. Meanwhile, remove rosemary and bay leaves from cooked beans. Put leek into the slow cooker with the beans. Carefully squeeze out cooked garlic cloves into beans. Using an immersion blender, puree the beans until smooth. Spoon onto a deep plate. Top with freshly cracked pepper.
On top of the bean puree, place a slice of grilled eggplant, top with a slice of mozzarella, tomato, chopped basil, repeat. Top with freshly grated Parmesan cheese and garnish with basil.