Coat a large Dutch oven with cooking spray, and place over medium-high heat until hot. Add onion and garlic; sauté 5 minutes. Add corn cobs and broth; bring to a boil. Reduce heat, and simmer, uncovered, 1 hour. Remove from heat; cover and let stand 30 minutes. Strain mixture through a sieve in a large bowl; discard solids.
Shortcut: Substitute 3 (14 1/2-ounce) cans vegetable broth for the 5 cups Corn Stock in the Hopi Indian Stew With Posole and the Tortilla Soup.