Place the masa in a large bowl and add flour, lard, baking powder and salt. Moisten your hands and knead for 5 minutes. Cover with a damp cloth and let rest for 10 minutes.
Form the masa into 12 balls. Line a tortilla press with plastic wrap, place a ball of masa in the center and cover with another piece of plastic. Press lightly to form a 4-in (10 cm) circles. Peel the plastic from the top of the tortilla and spread a spoonful of filling (recipes follow) on the tortilla in a half circle, leaving a 1/2 in (1-cm) margin around the edge. Fold the tortilla in half and remove the plastic from the bottom. Press the edges of the quesadillas to seal.
In a skillet heat 1/2 in (1 cm) oil to 375°F (190°C). Fry the quesadillas, 2 at a time, for 2 to 3 minutes on each side or until lightly browned. Do not let them stick together as they fry.
Serve with guacamole and salsa mexicana.
Relleno de queso (Cheese Filling): Place a spoonful of cheese and a sprig of epazote in each quesadilla.
Relleno de Papa con Chorizo (Potato and Chorizo Filling): Cook the potatoes in boiling salted water. When they are tender , drain and place in a bowl. Mash slightly with a fork.
Heat a skillet, add the chorizo and cook over low heat for 8 to 10 minutes.
Add the chorizo to the potatoes. Moisten with a tablespoon of fat rendered from the chorizo and mix well.
Relleno de Flor de Calabaza (Squash Blossom Filling): Remove the stems and pistils from the flowers. Rinse with water, drain and chop coarsely.
Heat the oil in a skillet, add the onion and garlic and sauté for 2 minutes. Add the tomato, stir and heat for 3 minutes or until the mixture comes to a boil. Add the flower, chile poblano, epazote and salt. Cook, uncovered, over medium heat until flowers are soft and the excess liquid has evaporated, about 4 minutes.