Slice the leeks in half lengthwise, using all the white part of the bunch, and some of the lighter green. Submerge the cut leeks in a bowl of cold, salted water. Agitate and remove from the water.
Separate the freshly shucked oysters from their water and save both.
Heat a large skillet on a medium heat. Add 4 tablespoons of butter, onions, leeks and garlic. Sauté until transparent. 
Next, add the cream sherry and the liquid from the freshly shucked oysters. Reduce until almost all of the liquid is gone.
Next, add the heavy whipping cream and continue to cook. Stir constantly with a whisk. Reduce until thickened to a porridge-like consistency (about 5 minutes). Then add the Tabasco sauce, salt, and pepper.
Last, add the Parmesan cheese and stir. Remove from the heat.
In a second skillet, sauté the fresh-shucked oysters with 2 tablespoons of butter for approximately 3 to 5 minutes. Drain off excess liquid. Add the sautéed oysters to the sauce and stir.
Serve the warm oysters and sauce over the bread.