Start this recipe by making the white sauce and allow to cool down completely for 30 minutes. Mix the ingredients of the white sauce packet with 200ml milk and pour into a saucepan. Heat till boiling mixing continuously until thick. (Add in any more milk if necessary but you want it thick not runny) Allow to cool for 30 minutes. Divide into 2 bowls. In one, mix in the spinach and parmesan, reserving 1 tbsp of parmesan. Use half to fill one croissant and spread the remaining on top. Sprinkle over the remaining tbsp. of parmesan. In the second bowl mix in the chopped ham and half of the grated Cheddar. Again use half to fill the croissant and spread the remaining on top. Finish off with the remaining Cheddar on top. Place into the oven at 200°C or grill to just heat through and brown the tops. Serve whilst still warm.