Preheat oven to 350 degrees F (175 degrees C). Grease and flour an 8x8 inch pan.
In a large bowl, cream together the butter and sugar until light and fluffy. Beat in the eggs one at a time, then stir in the vanilla. Combine the flour, baking powder, baking soda and salt; stir into the creamed mixture. Fold in the white chocolate chips and walnuts. Spread evenly into the prepared pan.
Bake for 25 to 30 minutes in the preheated oven. A toothpick inserted into the center should come out clean. Allow to cool before frosting.
To Make Frosting: In a medium saucepan, heat the cream over low heat until it just begins to simmer. Remove from heat and stir in the white chocolate chips until melted and smooth. Allow to cool and spread over cooled brownies.
Interesting Facts
White chocolate is not a true chocolate because it does not contain cocoa solids, which are found in regular chocolate.
Walnuts are a good source of protein, dietary fiber, Omega 3 fatty acids and antioxidants.
White chocolate is made from cocoa butter, sugar, milk and vanilla.