Heat oven to 375°F. Lightly spray round 2-quart glass casserole with cooking spray: set aside.

In large saucepan, heat olive oil over medium-high heat. Add onion and celery; cook 2 to 3 minutes or until onion is translucent. Add 1 ¼ cups broth; bring to a boil. Stir in couscous; cover. Remove from heat; let stand 5 minutes.

In large bowl, combine 1 cup broth, egg, sugar, sage and black pepper; mix well and set aside.

Fluff prepared couscous lightly with a fork. Stir in cranberries and walnuts; add to egg mixture, tossing until well-combined.

Spoon into prepared casserole; bake uncovered about 40 minutes or until toothpick inserted in center comes out clean.