Lightly grease the loaf tin and line with greaseproof paper.
Then, in a large bowl, whisk together the eggs, sugar, cream, lemon zest, rum, salt and melted butter.
Sift the flour and baking powder together, then whisk into the egg mixture until smooth, spooning the mixture into the loaf tin and gently level the surface.
Bake for 50 minutes, turning the tin around halfway through cooking. To test the cake, insert a small knife into the middle – if it comes out clean, the cake is cooked.
Turn out onto a wire rack and leave to cool for 10 minutes.
Lightly brush the cake all over with the warm jam. The jam creates a barrier, so the lemon glaze is not absorbed. Leave for 5 minutes.
Now mix the lemon zest and juice with the icing sugar in a small pan and warm over a low heat to 35°C, until smooth. If the glaze is any hotter, it will re-crystallise, losing its shine and crispness.
Brush the lemon glaze evenly over the top and sides of the cake and leave for a few minutes to set.
Finally, place the cake on a baking tray in the oven, turn off the heat and leave for 3–5 minutes to dry the glaze – it will become translucent. Allow to cool before slicing.