In a large saucepan, bring butter and water to a boil. Remove from the heat; stir in the flour, sugar, eggs, sour cream, almond extract, baking soda and salt until smooth.
Pour into a greased 15-in. x 10-in. x 1-in. baking pan. Bake at 375 degrees F for 20 to 22 minutes or until a toothpick inserted near the center comes out clean and cake is golden brown. Cool for 20 minutes.
For frosting, in a large saucepan, combine butter and milk. Bring to a boil. Remove from the heat; stir in sugar and extract. Stir in walnuts; spread over warm cake.