Preheat the oven to 180C (350F). Grease and line your cake tins. You can use four shallow tins or 2 deep ones. The taller cakes will require slightly longer baking time. Dust with flour and shake off any excess.
Put the eggs and sugar in a large bowl and lightly whisk together. Place the bowl over a pan of barely simmering water, making sure that the bottom of the bowl doesn't touch the water.
Whisk the eggs and sugar with an electric hand mixer until the mixture is lukewarm, 5-10 minutes.
Remove the pan from the heat, and without removing the bowl, continue to whisk until the batter almost triples in volume. The batter should fall from the whisk in a thick ribbon.
Sift the flour over the batter in two or three stages, adding alternately with the cooled melted butter. Remember to add the orange zest and oil.
Use a large spatula to gently fold the ingredients together – starting from the centre of the bowl draw the spatula along the bottom of the bowl and bring up to skim the sides.
Continue until the ingredients are all mixed in – take care that the butter is well blended in as it tends to sink to the bottom!
Divide the batter between your tins and bake 15-20 minutes from a small shallow cake and 20-25 minutes for a cake baked in a deep tin that is to be sliced in half.
The cakes will be done when the top is springy and the edges have began to shrink from the sides. Cool on a wire rack for 5 minutes, then carefully turn out from the tins. If you are slicing the taller cakes in half, wait until the have cooled down and slice with a serrated knife.
Strain the orange juice to remove any pulp, then put with the sugar in a small pan. Simmer over low heat for about 10-15 minutes, until the sugar has dissolved and the syrup is slightly reduced.
Brush the syrup over the cake layers while it is still a little warm.
Sandwich the cakes with a generous amount of orange marmalade.
Prepare the chocolate glaze: put the chopped chocolate in a large bowl. Heat the milk and golden syrup in a small pan until almost boiling.
Pour over the chocolate and leave to stand for a couple of minutes. Use a small balloon whisk to gently stir the chocolate, starting in the centre of the bowl and very gently and slowly increase the stirring motion until the chocolate has melted completely into a smooth glossy glaze.
Stir in the butter until it has melted into the glaze and leave it to cool until it thickens slightly.
Use a spoon to slowly pour the glaze until it starts to drip down the sides of the cake.
Decorate with thinly sliced cumquats or candied peel if you like. The cake is best consumed soon after it is assembled.