Combine fruit, jam and liqueur in a large bowl, cover and stand at room temperature overnight or for up to 1 week (I left mine for 4 days).
Preheat oven to 150°C (300°F). Line base and side(s) of a deep 22cm (9-inch) round or a deep 19cm (8-inch) square cake pan with 1 layer of brown paper and 3 layers of baking paper extending paper 5cm (2 inches) above side(s) of pan.
Beat butter, spread and sugar in a small bowl with an electric mixer until just combined (do not overbeat as this will soften the mixture too much; you need a robust mixture to carry all the fruit). Add eggs, one at a time, beating until just combined between additions.
Stir butter mixture into fruit mixture, then stir in the sifted dry ingredients and nuts (it will be very stiff, so I suggest you use a large metal spoon).
Spread mixture into pan and level off the surface.
Bake about 3-1/2 hours or until cooked when tested (after 1.5 hours I turned the temp down to 130°C (265°F) to ensure the cake didn’t overbake).
As soon as the cake is out of the oven, poke holes through it and brush it with 1/4 cup of the extra liqueur.
Cover hot cake with foil, wrap in a clean towel, and cool in pan overnight. (NB: If you intend to store the cake once the cake has cooled, cover firstly in layers of baking paper, then a couple of layers of tin foil and place in a sealed container in a cool, dry place. You can brush on extra liqueur once a week if storing for several weeks).
When ready to decorate, brush cake all over with remaining 1/4 cup of liqueur. Knead the ready-made icing on a surface dusted with a little sifted cornflour until it loses its stickiness. Roll icing into a round large enough to cover cake. Using a rolling pin, carefully lift icing over cake. Dust hands with cornflour, and use to mould icing over the top and sides of cake, gently rub icing with hands until smooth. Trim the icing neatly around the base (I didn’t bother icing the whole cake and just covered the top). Stand cake at room temperature to dry overnight.
Re-roll any scraps of icing into a 6mm (¼-inch) thickness, using snowflake (or other preferred shape) cutters, cut out shapes to decorate the surface. Affix to the surface with a little brushed on water.