Remove from the heat, and transfer the clams with a slotted spoon to a rimmed baking sheet to cool. Cook just until the shells open, 7 to 9 minutes. When the water starts to bubble, add the clams in a single layer, and cover with a tight-fitting lid. Heat 2 tablespoons water in a straight-sided medium skillet over medium heat. Rinse the clams thoroughly under cold water. Transfer the clams to a strainer with a slotted spoon, leaving any sand at the bottom of the bowl. Add the clams, and let sit for 10 minutes. Stir together 8 cups cold water and the cornstarch in a large bowl.
