Veg varies in water content, so keep an eye on the cake near the end of cooking – it might take slightly less or slightly more time to cook.
Heat oven to 180C/160C fan/gas 4. Grease and line a 30 x 20cm baking or roasting tin with baking parchment. Mix the sultanas and zest and juice from 1 orange (or 2 clementines), and microwave on High for 2 mins.
Mix the flour, caster sugar, spices, bicarb and pinch of salt into a large bowl. Mix the eggs with the melted butter and sultana mixture, then tip into the dry ingredients and stir in with a wooden spoon. Stir in the grated veg, and scrape into the tin. Bake for 35 - 40 mins, or until a skewer poked in the centre comes out clean. Cool in the tin.
Once cool sift the icing sugar into a bowl and stir in remaining orange zest plus enough juice to make a runny icing. Drizzle all over the cake and scatter with the crushed sugar cubes. Leave to set, then slice into 15 squares to serve.