Preheat the oven to 180C/ 160C Fan/Gas 4. Grease and line the base and sides of a 20cm round cake tin and a 15cm round cake tin.
Beat the spread with the sugar until smooth. In a separate bowl, stir together the eggs, milk and caramel flavouring. Stir the baking powder into the flour.
Mix 1⁄2 the egg mixture into the spread and sugar. Stir in 1⁄2 the flour, then mix in; repeat with the remaining eggs and flour. Divide the cake mixture between the 2 tins.
Bake for 1 hr-1 hr 10 mins until a skewer pushed into the middle of each cake comes out clean. Cool in the tins for 15 mins, then cool completely on a wire rack.
Meanwhile, in a large bowl, stir the vanilla frosting into the crumbled Madeira cake until it forms a soft dough. Divide into 3.
For the large turrets, line the 2 plastic tumblers with clingfilm and fill each with 1⁄3 of the Madeira mixture, pressing in firmly.
For the smaller turrets, divide the remaining 1⁄3 into 2 and roll into short, thick logs. Chill all turrets for 1 hr.
Put the digestives in a zip-seal bag and bash to crumbs with a rolling pin. Spread a thin layer of the caramel frosting on the cake board and sprinkle with crumbs to make ‘sand'.
Turn the turrets out of the tumblers and roll in the biscuit crumbs. Coat the smaller turrets and the fudge cubes in crumbs.
Cover the larger sponge with a thin layer of frosting, then gently press on a layer of crumbs for a sandy effect.
Put this sponge on the cake board, arrange the smaller sponge on top and cover in crumbs as before.
Arrange the 2 large turrets at the front. Place the 2 small turrets on top.
Carefully trim down the waffle cones to fit the tops of the turrets. Press gently into place, then top each turret with a flag. Press a finger biscuit onto the front of each turret for arrow slits.
Press 7 of the crumbed fudge cubes into the front of the bottom sponge to create the arched doorway. Arrange the rest around the top of each sponge, with gaps, for the battlements.
Decorate the base of the cake with the Maoam Roxx sweets and sprinkle any leftover crumbs around the cake.