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 23 cm square pan. Spread batter evenly in pan. Bake at 160ÂșC 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.