Preheat the oven to 350 degrees. Grease an 9x13 inch baking pan.
Combine the butter, sugar and tofu in the in jar of a high speed blender, blend until smooth and glossy on high speed, add vanilla at the end of the blending process.
In a medium mixing bowl combine the flour, cocoa powder, baking powder and salt. Mix well then add the blended tofu mixture and stir by hand until well blended. Add the walnuts, stir well then spread the mixture evenly in the prepared baking dish and bake for 30-40 minutes or until a knife inserted comes out clean and the top is firm. Let cool and top with vegan chocolate frosting.
In a medium saucepan bring the sugar, cream and butter to a boil stirring constantly. Add the chocolate and continue stirring until thickened 4-5 minutes. Remove from heat and stir in the vanilla and sea salt. Let cool then beat until smooth. Spread over cooled brownies and top with chopped walnuts.