Rinse jalapeños under cool water and pat dry. Leave stems on for easy handling. For less heat, cut out seeds and white ribs. For full spice, leave seeds in. Halve lengthwise or leave whole. Space them out in the skillet—no crowding. Set a plate nearby for finished peppers.

Heat a large skillet over medium-high heat for 1–2 minutes until very hot. Add about 1 tbsp oil and let it shimmer. Place jalapeños in a single layer—cut-side down if halved, flat if whole. Don't move them for 2–3 minutes until skin blisters and chars. Flip and cook the other side 2–3 minutes until blackened all over. Whole peppers: rotate to char all sides, 6–10 minutes total. Peppers should show dark char spots but stay slightly firm inside. Work in batches to avoid crowding. Transfer to a plate as each batch finishes.

Let peppers rest on a plate for 2–3 minutes. Optionally, place in a paper or plastic bag for 5 minutes to steam and loosen skins. Serve warm in tacos, over rice, or as a side. Refrigerate leftovers up to 2 days; reheat gently.