Tacos de Calabacitas a la Mexicana (Mexican-Style Zucchini Tacos)

Ingredients

1 1/2 tablespoons vegetable oil
1 medium white onion, chopped
1 pound (2 medium-large round or 6 to 8 plum) ripe tomatoes, roughly chopped OR two-thirds of a 28-ounce can good-quality fire-roasted tomatoes
2 garlic cloves, peeled
2 large fresh poblano chiles
1 large ear corn, husked and kernels cut off (about 1 cup) OR 1 cup frozen corn
4 medium (about 1 1/2 pounds total) zucchini—or use the Mexican round or teardrop-shaped, light green calabacitas—trimmed and cut into 1/2-inch cubes (about 5 cups cubes)
1 sprig epazote, leaves roughly chopped OR 3 tablespoons chopped fresh cilantro
2/3 cup Mexican crema, crème fraîche or heavy (whipping) cream
1/2 cupcrumbled Mexican queso fresco, or other crumble fresh cheese, such as salted pressed farmer’s cheese or feta
24 warm fresh corn tortillas

Preparing the flavoring base. Measure the oil into a large (12-inch) skillet set over medium-high heat. Add the onion and cook, stirring frequently, until richly browned, about 8 minutes. While the onion is cooking, coarsely puree the tomatoes in a food processor or blender. Add the garlic to the browned onion, cook 1 minute, stirring, then add the tomatoes. Reduce the heat to medium-low and cook, stirring occasionally, for 5 minutes. (Cover the skillet if you think it’s reducing and thickening too fast.) Remove from the heat.
Roasting the chiles. Roast the poblanos directly over a gas flame or on a baking sheet 4 inches below a very hot broiler, turning regularly until the skin has blistered and blackened on all sides, about 5 minutes for open flame, about 10 minutes for broiler. Cover with a kitchen towel and let stand 5 minutes. Rub off the blackened skin, then pull out the stem and seed pod. Rinse briefly to remove stray seeds and bits of skin. Slice into 1/2-inch strips.
Finishing the dish. Uncover the skillet and raise the heat to medium-high. Stir in the poblanos, corn, zucchini, epazote (or cilantro) and the crema (or one of its stand-ins). Cook, stirring frequently, until the zucchini is crisp-tender and the liquid has thickened enough to coat the vegetables nicely, about 8 minutes. Taste and season with salt, usually about 1 teaspoon. Serve in a decorative bowl, sprinkle with the crumbled cheese and pass the hot tortillas separately for do-it-yourself tacos.