Preheat oven to 350 degrees F (175 degrees C). Grease and flour a 9 inch square pan. In a saucepan, combine water and raisins. Bring to a boil and cook for 5 minutes. Remove from heat and stir in chopped dates and baking soda. Set aside.
In a large bowl, cream together 1/2 cup butter and 3/4 cup white sugar until light and fluffy. Beat in the eggs one at a time, then stir in the vanilla. Beat in the flour, salt and date mixture. Pour batter into prepared pan.
Bake in the preheated oven for 45 minutes, or until a toothpick inserted into the center of the cake comes out clean. Remove cake from oven, and set oven to Broil.
Make Topping: In a saucepan, melt 4 tablespoons of butter. Stir in brown sugar, cream and chopped nuts. Spread mixture over warm cake and place under broiler until lightly browned, about 3 minutes. Watch carefully – it burns easily under the broiler. Cool before serving.