Combine butter, sugar, eggs and vanilla
Beat 5 minutes at high speed until light and fluffy.
Blend in chocolate.
Mix four with soda, an salt
Add to creamed mixture alternately with ice water.
Beat after each addition ending with flour.
Bake in a greased and floured 13?x 9? inch pan, line pan with waxpaper for easy removal.
Bake for 25-30 minutes until top springs back.
After cake has cooled, place in freezer until quite firm but not totally frozen solid. This will make it easier to slice. Place on a cookie sheet. Using a long serrated knife cut cake horizontally. (*There are some ice cream companies who still make the 1/2 gallon squares of ice cream. It is too difficult to try the oval or round tubs.)
Slice cake horizontally into two equal layers. (Hint, hint: if you put toothpicks equally centered all around the cake you can cut it evenly).
Slice ice cream into 1 inch slices and place over bottom half of cake.
Place top layer on ice cream and return to freezer.
When cake is fully frozen remove cake from pan onto a cookie sheet.
Prepare fudge sauce (see below)
When ready to serve, remove cake and let stand about 20-30 minutes to soften.
Slice into desired pieces and top with hot fudge sauce.