Combine first 8 ingredients with electric mixer on medium-high. Beat 3 minutes scraping down sides of bowl often. Remove beaters. Stir in last 3 ingredients. Grease and flour 9" square pan. Spread batter evenly in pan. Bake at 325~ about 50 minutes. Cool in pan about 30 minutes. Frost with Cream Cheese Frosting and sprinkle with additional walnuts. ICING-Cream the cream cheese with the butter until light and fluffy, using medium-high speed of electric mixer. Add half of the sugar, increasing speed to high. Add extract and peel and beat about 1 minute. Scrape down sides of bowl often. Resume beating adding remaining powdered sugar. Beat smooth. Frost sides and top of cake.