Step 1
Cut pork into 3 chunks and place in a large saucepan. Add onion garlic bay leaves and salt and cover with water. Bring to a boil; skim foam from surface. Reduce heat cover and simmer for 1 hour. Remove pork and let cool. Strain broth and reserve.
Step 2
Bring a pot of water to a boil while pork is cooking. Add tomatoes arbol chiles and guajillo chiles and boil until chiles are soft about 5 minutes. Remove with a slotted spoon reserving cooking water and allow to cool.
Step 3
Place corn husks in a bowl cover with boiling water and soak for 30 to 60 minutes. Drain place on a work surface and cover with a clean damp towel.
Step 4
Combine tomatoes 1/2 cup cooking water chiles de arbol guajillo chiles and cornstarch in a blender; blend until smooth. Strain tomato sauce through a fine-mesh sieve.
Step 5
Beat lard with an electric mixer in a large bowl until fluffy. Combine masa 1 cup reserved pork broth 1 tablespoon salt and baking powder in a separate bowl and mix until smooth. Add masa mixture to lard and mix until it has a smooth cookie dough consistency. Test if the masa is ready by dropping a small ball of masa into a glass of cold water; if it floats it's ready if not keep beating for a little longer.
Step 6
Shred cooled pork with 2 forks.
Step 7
Select 1 wide corn husk or 2 small ones. Spread about 2 tablespoons masa mixture onto the the corn husk filling it up to 2 inches from the bottom and 1/4 inch from the top. Add 1 tablespoon of the tomato sauce and pork down the center of the masa mixture. Fold sides of husk together 1 over the other. Fold the bottom of the husk over the seam of the 2 folded sides. Repeat with remaining husks.
Step 8
Place a steamer insert into a saucepan and fill with water to just below the bottom of the steamer. Bring water to a boil. Add tamales with the open side up and cook until filling is heated through and separates from the husk about 1 hour. Let tamales rest for 15 minutes before serving.