Preheat oven to 150 degrees C.
Grease a 20cm round cake tin then line the bottom with baking paper. Spread the 5 teaspoons of caster sugar evenly over the bottom of the tin. Lay a third of the orange slices over the sugar, allowing them to overlap.
In a medium bowl, cream together the butter and sugar then beat in eggs, one at a time. Sift together the flour, salt and cinnamon. Stir into the egg mixture. Fold in ground almonds.
Spoon in about 1/3 of the cake batter into the prepared cake tin then lay 1/3 of the orange slices over the top. Repeat twice, until all batter and oranges are used. Place in preheated oven and bake for 2 hours.
Allow to cool then place serving plate upside down over the top, flip over then shimmy cake on to plate. Brush top with marmalade glaze made form heating the water and marmalade. Serve and enjoy.