Stuffed Tomatoes in Puff Pastry

INGREDIENTS

• 6 small vine-ripened tomatoes
• Salt
• 1 sheet frozen puff pastry, (9 1/4- by- 9 1/2 inches), thawed
• 1 tablespoon olive oil
• 1 small onion, coarsely chopped
• 1 small celery stalk, cut into thin half-moons (1/3 cup)
• 8 ounces sweet Italian sausage, casings removed, crumbled
• 2 tablespoons finely chopped fresh flat-leaf parsley
• 1/2 cup finely grated Parmesan cheese
• 1 large egg
• 1 tablespoon heavy cream