With your hands, work the salt into the masa and divide into 20-22 walnut-sized balls. Press them into rounds about 3 inches across and ⅛ inch thick. Set them side by side (not stacked) on baking sheets as they are shaped, covering them with a damp cloth.

Lightly grease a griddle or large cast-iron skillet and place over medium-high heat until a drop of water sizzles on contact. Have ready a basket lined with tea towels. Now you must work quickly, because the masa will be supple enough to shape for only a few seconds after baking. Place two of the prepared masa rounds on the hot griddle and bake for about 1½ minutes, until the edges shrink away slightly from the pan and lose their raw look. Turn and cook the other side for another 1-1½ minutes. Remove to a plate or work surface; while they are still hot, quickly pinch up the edges into a slightly raised rim. Place them in the basket and cover snugly with the towels. Continue with the remaining masa rounds, two at a time.

In a small saucepan, heat the lard over medium heat until hot but not quite rippling. When ready to serve, arrange the picadas on a griddle and brush with the melted lard. Top each picada with about 1 tablespoon of Salsa verde de aguacate. Scatter some of the cheese over the sauce and top with a swirl of crema and optional chopped onion.