Turn two stove-top burners to high and roast the poblano chiles on the racks of the burners (or directly on the element of an electric stove), turning frequently with tongs, until they are blistered and charred all over, 4 to 6 minutes. Put the poblanos in a bowl and cover with a plate to sweat for 15 to 20 minutes.
Rub off the skin from the roasted poblanos with a paper towel or your fingers (do not run the poblanos under water), then cut them open lengthwise. Cut out the stems, seed pods, and veins and lay the chiles flat. Wipe the chiles clean of seeds, discard the seeds, and slice the chiles into long ¼-inch-thick strips.
Heat the oil in a medium pan over medium heat until the oil shimmers, then add the onion, ¼ teaspoon of the salt, and the pepper, and cook until the onion is soft and translucent, about 5 minutes. Add the garlic, cook for a minute, then add the poblanos along with the remaining ¼ teaspoon of salt. Cook for 3 minutes or so, then add the crema and epazote.
Let it come to a simmer and cook, stirring, until the crema thickens slightly and coats the poblanos, about 3 minutes. Season to taste with salt.
Serve with tortillas topped with queso fresco and salsa.