Soak the clams in cold water for 20-30 minutes so they expel all sand and to clean them. Meanwhile, to make a beurre manie, soften 50g of the butter and mix in the flour to make a thick paste. Set aside. Drain the clams and rinse a couple of times, checking they are free of sand.
Heat a large pan with a lid over a high heat until hot. Tip in the clams and wine and cover. Shake the pan, then remove lid, remove the open clams and set aside, then replace lid and repeat.
Continue to cook the remaining clams this way until all clams have opened. When cool enough to handle, remove clams from their shells. Reserve some of the cooked clams in shells to garnish and roughly chop the rest of the clams. Pour the remaining cooking liquid through a sieve and into a clean pan, and then add the fish stock. Set aside.
In a heavy-based pan, heat the remaining butter over a medium heat. Add the onion, leek and garlic, and cook gently for 2-3 minutes until soft and translucent. Add the potato and cook for 5-8 minutes, until softened. Remove pan from the heat and add the clams and sweetcorn.
Meanwhile, bring the fish stock to the boil and whisk in the beurre manie in small pieces, whisking between each addition, and stirring until stock is thickened. Stir in the PHILLY Extra Light Cream for Cooking and the clam mixture and simmer for 2 minutes. Season, if liked, and serve scattered with parsley.