Rinse and de-stem the tomatoes. Roast the tomatoes in the oven at 200C for 20-30 minutes.
Add the roasted tomatoes to a blender along with 1/2 onion, 1 garlic clove, and only 1/4 of the jalapeno. Pulse blend until combined.
Taste for heat level. Add another 1/4 of the jalapeno if you want additional heat. Keep adding additional quarters of the jalapeno until you find a heat level that works for your taste buds.
Salt to taste. Serve immediately.
Store leftovers in an airtight container in the refrigerator.