Lobster Macaroni and Cheese

INGREDIENTS

• 1 cup chopped onion
• 2 tablespoons chopped fresh chives
• 4 tablespoons (1/2 stick) butter, divided
• 1/4 cup Cognac or brandy
• 2 tablespoons olive oil, divided
• 1 cup whipping cream
• 6 ounces fresh crabmeat, picked over
• 12 large shrimp, peeled, deveined, shells reserved
• 2 garlic cloves, peeled, flattened
• 3 cups water
• 3/4 cup chopped peeled carrots
• 1 Turkish bay leaf
• 1 1/2 cups grated Fontina cheese (about 6 ounces)
• 1 1 3/4- to 2-pound live lobster
• 8 ounces shell or gemelli pasta
• 3/4 cup chopped celery
• 2 tablespoons all purpose flour
• 1 tablespoon tomato paste