In a large bowl mix achiote, cumin, salt and shrimp. Mix well.
Heat 2 tablespoons olive oil in a 12-inch non-stick skillet over medium-high heat. Add half of the onion and cook, stirring frequently for 1 to 2 minutes, or until the onion is transparent. Stir in 1 clove finely minced garlic and cook for about 30 seconds. Add the shrimp and cook, stirring constantly, for about 4 to 6 minutes, or until they are brown on the edges and solid. Cover with foil and set aside.
In a small bowl mix the sour cream and milk. Cover with plastic wrap and place in the refrigerator.
In a blender, add the tomatillos, remaining onion, 2 garlic cloves, chicken broth, cilantro, chile, and salt. Blend on high for about 1 to 2 minutes, or until well incorporated.
Heat 1 tablespoon oil in a 3-quart sauce pan over medium high heat. Add the tomatillo salsa and cook for 3 to 5 minutes, or until salsa slightly thickens and the color has darkened to a deeper green.
Heat 2 tablespoons oil in a 12-inch skillet over medium heat. Place the corn tortillas, one at a time, and heat 20 seconds per side. As each tortilla gets heated, transfer to a sauce pan with tomatillo sauce and carefully dip and then place it on a platter. Fill with 2 to 3 tablespoons shrimp. Roll the tortilla to form enchiladas. Repeat for all the remaining tortillas.
Pour the tomatillo salsa on top of the enchiladas. Drizzle with the crema. Sprinkle with cheese. Garnish as desired and serve.