Place dried 40 pieces hojas de maíz in a large pot or bucket. Cover completely with very hot water and weigh them down with a heavy plate or bowl. Soak for at least 1 hour, or until fully pliable and soft. Drain, rinse, and pat dry before using. Keep them covered with a damp towel as you work.

Place the 3 lb espaldilla de cerdo chunks in a large pot. Add the halved 1 cebolla blanca, smashed 6 dientes de ajo aplastados, 2 tsp sal kosher, and 1 tsp granos de pimienta negra. Cover with cold water by about 2 inches. Bring to a boil over high heat, skimming any foam that rises to the surface.

Reduce heat to low, partially cover, and simmer until the 3 lb espaldilla de cerdo is very tender and easily shredded with a fork, about 2 to 2.5 hours. Remove the 3 lb espaldilla de cerdo and set aside to cool. Strain and RESERVE the 2 cups caldo de cerdo — you will need 5 cups total for the masa and chile sauce. Let the 2 cups caldo de cerdo cool slightly and skim off excess fat.

Once the 3 lb espaldilla de cerdo is cool enough to handle, shred it into bite-sized pieces using two forks or your hands, discarding any large pieces of fat or bone. Set the shredded 3 lb espaldilla de cerdo aside.

While the 3 lb espaldilla de cerdo simmers, toast the 6 chiles guajillo secos enteros sin tallos ni semillas and 3 chiles ancho secos enteros sin tallos ni semillas in a dry skillet over medium heat for about 30 seconds per side, pressing them flat, until fragrant and slightly darkened. Do not burn them or the sauce will taste bitter.

Transfer the toasted 6 chiles guajillo secos enteros sin tallos ni semillas and 3 chiles ancho secos enteros sin tallos ni semillas to a saucepan. Add enough water to cover and bring to a boil. Remove from heat and let soak for 20 minutes until softened.

Drain the 6 chiles guajillo secos enteros sin tallos ni semillas and 3 chiles ancho secos enteros sin tallos ni semillas and transfer them to a blender. Add the 6 dientes de ajo aplastados, 1 tsp comino, 1 tsp orégano, 2 tsp sal kosher, and 2 cups of the reserved warm 2 cups caldo de cerdo. Blend on high until completely smooth, about 1–2 minutes. Taste and adjust 2 tsp sal kosher as needed. If the sauce seems very thick, add a splash more 2 cups caldo de cerdo.

Heat 1 tbsp of manteca or 1 cup shortening in a saucepan over medium-high heat. Pour in the blended chile sauce carefully (it will splatter). Fry the sauce, stirring constantly, for 3–4 minutes until it deepens in color and thickens slightly. This step removes the raw chile flavor.

Add the shredded 3 lb espaldilla de cerdo to the red chile sauce and stir to coat thoroughly. The filling should be moist but not soupy. Taste and adjust seasoning. Set aside to cool slightly.

In the bowl of a stand mixer fitted with the paddle attachment (or a large mixing bowl with a hand mixer), beat the 1 cup manteca on medium-high speed until light and fluffy, about 3–4 minutes. This step is key to a light, airy masa — don't skip it.

In a separate large mixing bowl, whisk together the 4 cups harina de masa, 2 tsp sal kosher, and 1 ½ tsp polvo de hornear. Gradually add the warm reserved 2 cups caldo de cerdo and mix until a soft dough forms.

Add the masa dough to the whipped 1 cup manteca in 3–4 additions, beating on medium speed between each addition until fully combined. The finished masa should be soft, smooth, and spreadable — similar to thick peanut butter. To test: drop a small ball of masa into a glass (Large) of cold water. If it floats, the masa is ready. If it sinks, beat in a little more 1 cup manteca and test again.

Set up your assembly station: soaked 40 pieces hojas de maíz (covered with a damp towel), masa, and pork filling. Take one 40 pieces hojas de maíz and lay it flat with the wide end facing you. Using the back of a wooden spoon or a spatula, spread about 3 tbsp of masa onto the center of the husk, leaving a 1-inch border on the sides and a 2-inch border at the narrow (top) end.

Spoon about 2 tbsp of the pork filling down the center of the masa. Do not overfill — it makes folding difficult.

Fold one long side of the hojas de maíz over the filling so the masa edges meet and enclose the filling. Then fold the other long side over. Finally, fold the narrow (top) end of the husk up and under the tamale. The open bottom end stays open. Place the tamale seam-side down. Repeat with remaining husks, masa, and filling.

Fill a large steamer pot with about 2 inches of water. Line the steamer basket with extra 40 pieces hojas de maíz or a layer of parchment paper. Stand the tamales upright in the steamer, open end up, packing them snugly together so they support each other. If you have gaps, fill them with crumpled aluminum foil or extra 40 pieces hojas de maíz.

Cover the tamales with a layer of extra 40 pieces hojas de maíz, then place the lid tightly on the pot. Steam over medium heat for 75–90 minutes, checking the water level every 30 minutes and adding more boiling water as needed to prevent the pot from running dry.

The tamales are done when the masa pulls away cleanly from the 40 pieces hojas de maíz. Remove one tamale, let it rest for 5 minutes, then open it to test. If the masa is still sticky or wet, re-cover and steam for another 15 minutes. Let all tamales rest for 5–10 minutes before serving — they firm up as they cool slightly.