Preheat the oven to 425°F. Cut the potatoes into ⅛-inch-thick slices.
Combine the potatoes, cream, egg, one of the jalapeño peppers, thyme, rosemary, salt and pepper in a bowl and mix well.
Spoon half the potato mixture into an 8x8-inch baking dish. Sprinkle with half the Cheddar cheese, half the Monterey Jack cheese and the remaining jalapeño peppers.
Layer with the remaining potato mixture, remaining Cheddar cheese and remaining Monterey Jack cheese.
Bake for 20 minutes uncovered and an additional 40 minutes covered with foil.
Add additional cheese for a cheesier flavor. You may substitute Gruyère cheese for the Cheddar cheese and green onions for the jalapeño peppers.