Step 1: Simmer the potatoes in salted water to cover until tender, about 15 minutes. Drain, cool under running water, peel and cut into 1/4-inch dice.

Step 2: Heat the oil in a heavy medium-size skillet over medium. Add the onion and potato, and fry, stirring regularly to ensure that nothing sticks to the pan, until the mixture is richly browned, 10 to 15 minutes.

Step 3: While the potatoes are browning, seed the chiles and roughly chop. Stir them into the potato mixture with epazote and season with salt to taste. Remove the mixture from the heat and stir in the cheese.

Step 4: Fry corn tortillas in olive oil over medium heat. Fill with potato filling, fold in half, and serve with your favorite hot sauce.