Adjust the top rack in the oven to the highest level and set the oven to broil.
Add a layer of parchment paper to the cookie sheet/roasting tray.
Prep the ingredients for roasting.
Roughly chop half of the red onion.
Rinse tomatoes and jalapeno in water and pat dry with a paper towel
Place tomatoes, jalapeno, and chopped onions on top of parchment paper on the roasting tray.
Make sure to read the notes above to adjust the spiciness of the salsa.
Coat ingredients with olive oil.
Place the tray in the oven and set the timer for 10 minutes.
Remove large cilantro stems (small stems are okay) and roughly chop. Set aside.
Check the ingredients in the oven.
After 10 minutes, if the tomatoes and jalapeno skins are blistered and beginning to bubble under the skin and the onions are turning a light brown, stir the ingredients and place them back under the broiler for an additional 5 minutes. Continue to check ingredients to avoid burning. Add more time under the broiler as needed.
Remove the tray and ingredients from the oven. Place jalapeno on the cutting board.
Remove stem from jalapeno
If you desire medium spiced salsa, remove the seed and ribs from the jalapeno.
Gently slice the jalapeno open lengthwise ( from stem to bottom).
Use a spoon to gently scrape the seeds out.
Use the sharp end of the knife and gently remove the ribs inside. This can be done by gently slicing under each rib lengthwise and while pulling the rib.
The seeds and ribs carry the heat so make sure to wash your hands well with soap and warm water. You can also use disposable rubber gloves to remove seeds and ribs. This will ensure that the heat does not transfer to your hands.
Place the roasted tomatoes, red onions, and jalapeno in the blender/food processor.
Add the chopped cilantro, lime juice, and salt to the blender.
Blend ingredients on medium-high for 30 seconds.
Pour salsa into a serving dish or storage container.
Salsa will be warm and delicious.
If you prefer to have cold salsa, just place it in the refrigerator for at least 30 minutes or overnight.