For the Salsa Verde:

Combine tomatillos and 1 onion (peeled and roughly chopped) in a medium saucepan and cover with water. Bring to a boil over high heat then reduce to a simmer. Simmer until vegetables are completely softened, about 10 minutes, stirring occasionally to make sure all sides are softened. Drain vegetables then transfer to a blender. Add 3/4 of cilantro, a large pinch of salt, and 1 tablespoon lemon juice. Blend on medium speed until a chunky purée is formed, about 30 seconds. Transfer to a bowl, season to taste with more salt or lemon juice if necessary, and reserve. Cooled salsa can be stored in a sealed container in the refrigerator for up to 2 weeks.

For the Filling:

Finely mince half of remaining onion. Heat vegetable oil in a large saucepan over medium-high heat until shimmering. Add onion and garlic and cook, stirring frequently, until softened and light golden brown, about 4 minutes. Add cumin powder and cook, stirring, until fragrant, about 30 seconds. Add spinach in batches, stirring and allowing each batch to wilt before adding the next. Cook, stirring, until excess moisture has evaporated, about 7 minutes. Season to taste with salt and pepper. Transfer spinach to a colander to drain, pressing out excess moisture with a rubber spatula.

Transfer to a large bowl and fold in corn. Set aside.

For the Cashew Cream:

Combine cashews, remaining garlic clove, chipotle, stock, and vinegar in the jar of a blender. Blend on high speed, adding water or stock as necessary to reach a thick, pancake batter-like consistency. Continue blending until completely smooth, about 2 minutes. Season to taste with salt and transfer to a bowl.

To Assemble:

Set rack to 12 inches below broiler element and set broiler to high (alternatively, set oven to 475°F). Spread 1 1/2 cups of salsa verde across bottom of a 9 by 13-inch baking dish and transfer the rest to a shallow bowl. Working one tortilla at a time, dip tortillas into bowl of salsa verde, coating both sides thoroughly. Place on cutting board and top with 2 to 3 tablespoons of filling. Roll up tortilla and place edge-down in baking dish. Repeat until all tortillas are filled. Spread remaining salsa verde over top of tortillas. Spoon cashew cream over the baking dish in a single line down the center of each row of tortillas. Transfer to oven and bake until cashew cream is lightly browned and edges of tortillas are beginning to crisp, about 15 minutes. Thinly slice remaining half onion and roughly chop remaining cilantro. Sprinkle on top of enchiladas and serve.