Step 1: Prepare the Filling: Heat 2tsp oil in a pan, add the onions and cook till they translucent. Stir in the garlic cloves and cook for 30 seconds or until fragrant.
Add green pepper, corn and spinach. Cook covered till the veggies are tender, about 3~5 minutes.
Stir in cumin, chili powder, salt and pepper. Mix well and turn off the heat.
Step 2: Prepare the Corn Husks.
While the filling is cooling, prepare the corn husks. Dried corn husks need to be soaked in warm water prior to using to make them soft & pliable. Fill a deep pan with warm and soak the dried husks for 15~20 minutes.
Soak more husks than you need for the recipe because there might be rips and tears and also you need a few extra to line the steamer basket and tie the tamales. Once the husks are ready, then drain and keep them ready.
Step 3: Prepare the steaming equipment.
Set up the steaming basket. Fill the pot with 2~3" of water, or whatever level will stay below the steamer basket. Line the steamer basket with a few corn husks and keep ready.
Step 4: Prepare the Masa dough -- In a large mixing bowl, with a handheld mixer or in a stand mixer, cream together the shortening and margarine until creamy and light.
Sift in the masa harina, baking powder, garlic powder and salt, then continue to beat for about 3 minutes, until a sandy looking mixture forms.
Pour the vegetable stock into the masa mixture and continue to beat until all the liquid is absorbed and a fluffy dough forms, about 5 minutes.
The tamale dough should have a moist -- almost like mashed potato consistency - and should be easily spread with a rubber spatula. If the mixture seems too wet, then sprinkle in another tablespoon or two of masa harina. If too dry, then drizzle a tablespoon of vegetable stock until the desired consistency is reached. Use this dough right away for making tamales.
Step 5: Assemble the tamales -- Once Step 1~4 are done, get ready to make the tamales.
For each tamale, spread a generous ¼cup of dough down the center of a pliable soaked corn husk, leaving at least 1½" on either end. This will form a oblong of 4~5" wide and ⅜~½" thick. Spoon 1 generous tablespoon of filling down the center of the tamale dough, then top with a little of the grated cheese.
Grab both the edges of the corn husk that are not covered with dough. Bring the edges toward each other and push the sides of the masa dough together to encase the filling. Gently press the tamale to form a firm, solid tube shape. Tightly twist each end of the tamale wrapper and tightly tie each end with a soaked corn husk strip. You can even use kitchen twine to tie the tamales.
About half way through the tamale making, turn the steam basket on and get the water going. So that the steamer will be ready for you when the tamales are done.