From the island of Madeira in the Azores, off the coast of Portugal. Use a firm potato that will not get mushy when boiled. For the cheese, if you have access to Azorean Bravo cheese, use it, otherwise havarti is similar.
In a pot, boil the potatoes in salted water until for tender, about 20 minutes. Drain.
In a small bowl, combine just the egg yolk with 1/2 cup of the milk, mashing them into a "sauce".
Chop the egg whites and reserve.
Mix remaining milk, butter, onion, salt, pepper and hot sauce in a large bowl. Add the egg yolk mixture and the cooked potatoes to the bowl and turn to coat. Transfer to an oven-proof baking dish (lightly coated with nonstick cooking spray). Top with the cheese.
Bake in oven just long enough to turn golden on top. Serve with garnish of finely chopped parsley and chopped egg white.