Place husks in large pot or large bowl; add water to cover.
Place heavy plate on husks to keep submerged. Let stand until husks soften, turning occasionally, at least 3 hours and up to 1 day.
Preheat broiler. Line heavy baking sheet with foil. Arrange tomatillos on prepared sheet. Broil until blackened in spots, turning once, about 5 minutes per side.
Transfer tomatillos and any juices on sheet, garlic and chiles to blender. Blend until smooth puree forms.
Heat olive oil in medium saucepan over medium-high heat, add tomatillo puree and boil 5 minutes, stirring often. Add water.
Reduce heat to medium; simmer until sauce coats spoon thickly and reduced, stirring occasionally, about 20 minutes. Season with salt.
Add in shrimp and cilantro, cook for 5 minutes, cover and turn off the heat. Reserve.
Using a whisk, mix vegetable shortening and salt in a large bowl until fluffy. Beat in masa harina and water. If dough seems firm, beat in water, 2 tablespoons at a time (to soften)
Fill bottom of pot with steamer insert with enough water (about 2 inches) to reach bottom of insert.
Line bottom of insert with some softened corn husks. Tear 3 large husks into 1/4-inch-wide strips to use as ties and set aside.
Open 2 large husks on work surface. Spread 1/4 cup dough in center of each, leaving 2- to 3-inch plain border at narrow end of husk.
Spoon 2 tablespoons of filling in strip down center of each dough square. Fold long sides of husk and dough over filling to cover.
Fold up narrow end of husk. Tie folded portion with strip of husk to secure, leaving wide end of tamale open.
Stand tamales in steamer basket. Repeat with more husks, dough, and filling until all filling has been used. Bring the previously boiled water to the pot, cover and steam tamales until dough is firm to touch and separates easily from husk, adding more water to pot as necessary, about 45 minutes.