Place the poblano peppers directly over a gas flame, under a broiler, or on a very hot dry skillet. Turn frequently until the skins are blistered and blackened in patches all over, about 8–10 minutes. Transfer the roasted peppers to a bowl and cover tightly for 15 minutes. The steam loosens the skins and makes peeling easier. Covering the hot peppers tightly traps their own residual steam against the blistered skin, which is what loosens it from the flesh underneath — peppers left uncovered to cool will still peel, but with considerably more effort and torn skin left clinging to the pepper.

Gently rub off the blistered skins using your fingers or a paper towel. Do not rinse the peppers under water; it washes away flavour and makes them slippery. Cut one lengthwise slit in each pepper, keeping the stem attached. Carefully remove the seeds and large inner ribs without tearing the flesh. Pat the peppers dry inside and outside. This is a major turning point. Wet peppers will reject the flour and batter, and torn peppers will leak cheese into the oil. Rinsing under water might feel like the faster way to remove stubborn skin, but it strips away the peppers' own smoky, charred surface oils along with any remaining skin fragments — the flavour lost that way is a real and noticeable trade-off for the convenience.

Fill each poblano with about 70g white cheese strips. The pepper should look full but still close naturally. If needed, secure the opening with one or two toothpicks. Do not overstuff. Too much cheese will burst through the slit during frying. A pepper that closes naturally around its filling, without needing to be forced shut, is the visual cue that the amount of cheese is correct — overstuffed peppers put pressure on the slit from the inside out, and that pressure only increases as the cheese begins to melt in the hot oil.

Heat 30ml neutral oil in a large skillet or saucepan over medium-high heat. Add the Roma tomatoes cut-side down, onion wedges, and garlic. Cook for 6–8 minutes, turning occasionally, until the tomatoes soften and develop browned spots. Transfer the tomatoes, onion, and garlic to a blender. Add the chipotle peppers, adobo sauce, tomato paste, stock, cumin, oregano, salt, black pepper, and sugar if needed. Blend until smooth. Pour the sauce into a saucepan and simmer uncovered for 15–20 minutes, stirring occasionally, until vivid red, slightly thickened, and glossy. The sauce should be loose enough to pool around the peppers, not thick like paste. Taste and adjust salt. Browning the tomatoes cut-side down before blending concentrates their sugars and adds a light roasted character that a purely raw-blended tomato sauce wouldn't have — this step is quick but meaningfully deepens the final sauce's flavour.

Spread 60g flour on a plate. Lightly dust each stuffed poblano with flour, shaking off the excess. The flour layer should be thin and dry, just enough to help the egg batter cling. The flour here serves the same purpose as a dry dredge does for a battered fish — it gives the wet batter a slightly textured surface to grip, rather than sliding off the pepper's naturally smooth, roasted skin.

In a clean bowl, beat the egg whites with cream of tartar or lime juice until stiff glossy peaks form. In a separate bowl, whisk the egg yolks with salt and 30g flour until smooth. Gently fold the yolk mixture into the beaten whites in 2 additions. Do not deflate the batter. It should be airy, thick, and spoonable, not runny. Make the batter right before frying. If it sits too long, it collapses. The cream of tartar or lime juice stabilises the whipped whites' protein structure, helping them hold their air longer, but that stability is still temporary — folding gently in two additions, rather than one aggressive mix, is what keeps as much of that trapped air intact as possible going into the fry.

Heat 1–1.5cm neutral oil in a wide skillet over medium heat to about 170–175°C. The oil should shimmer, and a drop of batter should sizzle immediately without smoking. Dip one stuffed poblano into the egg batter, coating it fully. Carefully lay it into the hot oil seam-side up or slightly to the side. Spoon a little extra batter over any exposed areas if needed. Fry for 2–3 minutes per side, turning gently, until the batter is golden, puffed, and slightly irregular. Transfer to a rack or paper towel-lined tray. Repeat with the remaining peppers, working in batches. Do not crowd the skillet. Crowding drops the oil temperature and gives greasy, pale batter instead of a golden crust. Laying the pepper seam-side up or to the side, rather than seam-side down, keeps the cheese-filled opening away from direct contact with the hot oil for as long as possible, reducing the chance of cheese leaking out before the batter has set around it.

Spread most of the tomato-chipotle sauce in a wide pan or baking dish. Place the fried chiles rellenos into the sauce and warm gently for 3–5 minutes, spooning a little sauce around the sides but not drowning the golden batter. The sauce should pool around the peppers and lightly touch them. If you bury them completely, the batter turns soggy. This brief warming step is about bringing the fried peppers back up to serving temperature and letting the sauce's edges just touch the batter, not about cooking anything further — full submersion for even a few minutes will soften the crisp, puffed exterior that the frying stage worked to build.

Spoon tomato-chipotle sauce onto each plate. Place 2 chiles rellenos per serving over the sauce. Drizzle with loosened sour cream in thick white lines. Scatter fresh cilantro leaves over the top. Serve immediately while the batter is still tender and golden, the cheese is melted, and the red sauce is hot and glossy. The sour cream is loosened specifically so it drizzles in clean, visible lines rather than sitting as a thick dollop — that visual line work is part of the classic presentation, contributing to the deep green, red, and white colour story the dish is known for.