MAKE THE CAKE. Preheat the oven to 180°C (350°F/Gas 4). Beat the butter with the caster sugar in a mixing bowl, then add the flour, baking powder, eggs, milk and finally the Cognac. Beat for 1 minute with an electric beater until the mixture is creamy and uniform.
POUR THE BATTER INTO A BUTTERED AND FLOURED LOAF (BAR) TIN. Put the cake in the oven and bake for 35 minutes, until the top is firm and golden. To check whether the cake is cooke dall the way through, insert the blade of a knife into the middle; it should come out clean. Take the cake out of the oven.
MAKE THE ICING. Mix the sugar with the lemon juice, then pour this syrup over the cake while it’s still in its tin. Make sure you pour the lemon syrup over the cake while it is still hot! Let the cake cool and dry completely before turning it out and serving.