Preheat the oven to 350F. Butter 2 soufflÄ dishes. Put the milk, salt and pepper in a medium casserole and scold over a moderate heat. In a large saucepan melt the butter. Whisk in the potato or cornstarch and flour and cook for 2 minutes, whisking constantly. Pour in the scalded milk and bring to a boil, whisking constantly. Remove the pan from the heat and whisk in the egg yolks, 2 at a time. Stir in the grated cheese. Whisk the egg whites to stiff peaks in a copper bowl. Fold the beaten egg whites into the cheese mixture until uniformly mixed. Fill the dishes to the top and run your finger around the edge of each dish to make a small indentation. Bake for 15 minutes. If the top is browning too quickly, cover with a paper towel. Continue baking for 10 minutes.
