1.Preheat the oven to moderate (180°C/160°C fan-forced). Grease a 25cm x 35cm rectangular baking dish. Line base and sides with baking paper, bringing paper 5cm above edges of dish.
2.Combine dates and water in a medium saucepan; bring to the boil. Remove from the heat, add soda; stand for 5 minutes. Blend or process until smooth.
3.Cream butter and sugar in a large bowl with an electric mixer until well combined. Beat in the eggs, one at a time, beating until just combined between each addition. Stir in the sifted flour and date mixture.
4.Spread into prepared pan; sprinkle evenly with the nuts. Bake in a moderate oven for about 1 hour or until cooked when tested. Stand cake for 10 minutes before turning onto a wire rack.
5.Meanwhile, to make butterscotch sauce; combine all ingredients in a medium saucepan; stir over heat, without boiling, until sugar is dissolved. Simmer, stirring, for 3 minutes.
6.Brush surface of hot cake with 1/4 cup of butterscotch sauce, then serve with remaining sauce.
This recipe can be made two days ahead. Close to serving, wrap cake in foil and warm through in a moderately slow oven for approximately 20 minutes, or microwave individual servings. Suitable to freeze. Butterscotch sauce suitable to microwave.Note