Melt the butter and pour half of it into a rectangular tray and arrange the biscuits on top. Cut the pumpkin into pieces and then boil it for 30- odd minutes. Mash it and let it cool completely.
Beat the eggs, sugar and flour with the baking powder and mix the remaining butter in, add the cold mashed pumpkin and chopped walnuts. Pour the mixture over the biscuits in the tray.
Put the cake with pumpkin and biscuits to bake in moderately heated oven, checking for readiness with a stick. The finished cake can be sprinkled with powdered sugar.