Preheat oven to 350 degrees F (175 degrees C). Grease and flour a 9x5 inch loaf pan. In a saucepan over medium heat, bring dates and water to a boil. Stir in 1/2 cup butter and 1 cup sugar until melted. Remove from heat and stir in baking soda. Let cool for 10 minutes.
Place date mixture into a large bowl. Blend in flour, eggs and vanilla. Stir in chopped walnuts. Pour batter into prepared pan.
Bake in the preheated oven for 50 to 60 minutes, or until a toothpick inserted into the center of the cake comes out clean. Let cool in pan for 10 minutes, then turn out onto a wire rack and cool completely. Serve slices with Warm Sauce.
To make Warm Sauce: In a saucepan over medium heat, combine 1/4 cup butter with cream and brown sugar. Heat, stirring constantly, until mixture boils and sugar is dissolved.