For the Essex cockle chowder, heat the butter and oil in a large saucepan over a medium heat. When the butter is foaming, add the bacon and onion and fry for 4-5 minutes, or until the bacon is crisp and golden-brown and the onions have softened but not coloured. Remove the onions and bacon from the pan and set aside.
Add the wine to the pan the onions and bacon were cooked in and bring to a rolling boil.
If using fresh cockles, add them to the pan and boil for 3-4 minutes, or the shells have opened (discard any cockles that do not open during cooking). (NB: If using cooked cockles, skip this step.)
Remove the cockles from the pan using a slotted spoon, remove them from their shells and set aside to cool (reserve the cooking liquid).
Continue to boil the wine until it has reduced in volume by half. Set aside and keep warm.
Meanwhile, in a separate saucepan, parboil the potatoes in salted, boiling water for 5-6 minutes, or until just tender. Drain well and set aside.
Return the reduced cooking liquid to the heat, add the milk and parboiled potatoes and bring the mixture to a simmer. Continue to simmer until the potatoes are starting to fall apart.
Add the cooked cockles, parsley, thyme and cream to the mixture and return the cooked bacon and onion. Stir well. Heat through for 2-3 minutes, being careful not to overcook the cockles. Season, to taste, with sea salt flakes and ground white pepper.
Meanwhile, for the oysters Mornay, preheat the grill to its highest setting.
Melt the butter in a pan over a medium heat. Whisk in the flour and heat until a smooth paste forms.
Whisk in the milk a little at a time, making sure that each addition of milk has been incorporated into the mixture and the mixture has thickened slightly before adding the next.
When all of the milk has been incorporated into the mixture and a smooth, thick white sauce has formed, stir in half of the grated cheese and season, to taste, with salt and freshly ground black pepper.
Arrange the oysters, in their shells, in rows in a grill pan and spoon over the cheese sauce. Sprinkle over the remaining grated cheese and grill for 4-5 minutes, or until the cheese has melted and is golden-brown.
Just before serving, sprinkle over the parsley.
Meanwhile, for the traditional oysters, in a bowl, whisk together the red wine vinegar and shallots and set aside for five minutes.
Cover a serving platter with the ice. Push the shucked oysters (in their shells, with the shell juices) into the ice.
Serve the red wine and shallot mixture alongside in a ramekin, along with the lemon wedges and small bottles of Tabasco sauce and Worcestershire sauce.
To serve, spoon the Essex cockle chowder into 4-6 serving bowls. Place the bowls onto large serving plates and divide the oysters Mornay equally among the plates. Serve with the traditional oysters, sourdough bread and butter.