Preheat oven to 180 degrees C. Grease a 22cm square cake tin.
Base: In a large bowl mix the eggs and both sugars together. Blend in the nuts and sift the flour with the baking powder and salt. Add to egg mixture and blend well. Press into the bottom of the greased cake tin.
Bake for 20 to 25 minutes.
Topping: While the pastry bakes mix brown sugar, cream and cashews into the melted butter.
Spread over baked pastry and place under a grill for about 1 minute until topping bubbles and becomes brown. Cut into bars or squares while warm. Let cool in tin.