Start by greasing a ceramic or glass oven dish with butter and spread the lemon curd into the bottom. Put aside. Next, beat together the butter, sugar, lemon zest and juice till light and fluffy. Beat in the egg yolks, followed by the flour then the milk. Next, whip the 2 egg whites to stiff peaks and carefully fold into the cake mixture along with the blueberries. Do not overbeat as it will become heavy. Spoon the mixture over the lemon curd in the dish and place the whole thing into a large dish half filled with hot water. Bake in the oven at 200`c for approximately 40-45 minutes. Serve whilst still hot with a scoop of vanilla ice-cream on the side.