Only after baking this excellent and unusual recipe for some years did I discover that my thanks should go to the well-respected cookery writer, Katie Stewart, who first published it.
Sift the flour into a mixing bowl. Stir in the sugar, oats and walnuts. Add the butter in pieces and use a knife to cut it into the mixture. Beat the eggs with the zest and lemon juice and stir into the mixture for 1 minute. Spoon the mixture into the prepared cake tin and smooth level.
Bake in the preheated oven until cooked. Remove from the oven and leave the cake in the tin.