Preheat oven to 375 degrees
Grease 15 x 10 jelly roll pan; line pan with waxed paper and grease waxed paper
Sift flour, cocoa, baking powder and salt together, set aside
Beat eggs at high speed until thick and light yellow in color
Beat in granulated sugar a tablespoon at a time, beating constantly, until mixture is very thick
Beat in water and vanilla; fold in sifted dry ingredients until blended
Spread and batter evenly in prepared pan Bake at 375 degrees for 10 minutes or until center springs back when touched lightly with finger (it's important not to overcook)
Let cool for 10 minutes
Loosen cake around the pan edges using a sharp knife Invert pan onto waxed paper dusted with confectioner's sugar and remove pan and waxed paper
Make sure cake is just barely warm, then spread with cream filling
Roll jelly-roll fashion into a log
Place on serving plate
To make cream filling combine cream with sugar and beat at medium speed until peaks form; gradually beat in vanilla
To make chocolate butter frosting add water to bottom of double boiler and bring to easy boil
Break chocolate squares up into small pieces, and melt in top of double boiler In a medium sized mixing bowl, add soft butter, confectioner's sugar, milk, vanilla and pour in melted chocolate and mix on medium high speed until light and fluffy
