How to Make It
Preheat oven to 500°.
Brush tomato paste evenly over bones and shanks; place in a large roasting pan. Add celery, carrot, and onion to pan; lightly coat with cooking spray. Bake at 500° for 30 minutes.
Transfer bone mixture to a 6- or 8-quart pressure cooker; add peppercorns, bay leaves, and parsley. Pour 8 cups water over mixture. Close lid securely, and bring to high pressure over high heat. Reduce heat to medium or level needed to maintain high pressure; cook for 35 minutes. Remove from heat; release pressure through steam vent, or place cooker under cold running water to release pressure. Remove lid, and let stand for 20 minutes. Strain stock through a cheesecloth-lined sieve into a large bowl, pressing solids to release excess moisture. Discard solids. Cover and chill overnight. Skim solidified fat from surface; discard.
Note: Refrigerate stock for up to 1 week or freeze for up to 3 months.