1Preheat oven to 350 degrees F (175 degrees C). Grease and flour an 8 inch square cake pan.
2In a large bowl, mix the flour, sugar, baking soda and salt. Make a well in the center and add the egg, vanilla, mandarin oranges and 1/2 cup chopped nuts.
3Pour batter into an 8 inch square cake pan. Bake in the preheated oven for 30 to 35 minutes, or until a toothpick inserted into the cake comes out clean.
4While the cake is baking, prepare the sauce. In a medium saucepan, combine brown sugar, milk and butter. bring to a boil and stir in coconut and 1/2 cup walnuts. While still hot, pour over cake as soon as it comes out of the oven.