01 -
Heat a dry comal or cast-iron skillet over high heat until very hot. Add the whole tomatoes, the jalapeños cut side down, the onion half cut side down, and the unpeeled garlic cloves. Char without moving for 4 to 5 minutes, then turn everything and char another 3 to 4 minutes until blistered and softened in spots.
02 -
Peel the garlic. Add it to a blender with the charred onion half, cumin, a pinch of salt, and 1/2 cup water. Blend for 1 minute, then add the charred tomatoes and jalapeños. Pulse 2 to 3 times only, keeping the salsa coarse and rustic with visible texture. Set aside.
03 -
Pat the beef slices very dry with paper towels. Season both sides with salt, garlic powder, cumin, and black pepper. Heat the olive oil in a heavy skillet or Dutch oven over high heat until shimmering. Sear the beef in a single layer for about 1 minute per side until browned. Work in batches to avoid crowding the pan.
04 -
Return all the beef to the pan. Cover tightly, reduce the heat to its lowest setting, and cook for 25 to 30 minutes until fork-tender. If the pan dries out after 15 minutes, add 2 to 3 tablespoons of water to create steam and continue cooking.
05 -
Push the beef to one side of the pan. Add the remaining diced onion half and the potato cubes. Stir over moderate heat for 2 minutes to coat them in the pan drippings.
06 -
Pour in the ranchero salsa and enough water to just cover all the ingredients. Bring to a boil, then stir in the drained canned poblano peppers. Cover, reduce heat to medium-low, and cook for 10 to 12 minutes until the potatoes are fork-tender. Taste and adjust salt before serving.