Heat oven to 350°F. Grease bottom and sides of 13x9-inch pan with shortening; lightly flour.
In large bowl, beat flour, 1 1/4 cups of the sugar and remaining ingredients except rhubarb, nuts and whipped cream with electric mixer on low speed 1 minute, scraping bowl constantly. Beat on medium speed 2 minutes, scraping bowl occasionally. Stir in rhubarb. Pour into pan. Sprinkle with nuts and remaining 1/4 cup sugar.
Bake 45 to 50 minutes or until toothpick inserted in center comes out clean. Cool completely, about 1 hour. Serve with sweetened whipped cream.