This is the world's simplest salsa recipe, but you might be surprised at the flavor you get when making it in a molcajete (Mexican mortar and pestle). When making a homemade salsa, you'll find that crushing the veggies releases additional oils and creates an explosion of flavor that traditional store-bought salsas don't have. If you don't have a molcajete, I suggest you get one. What's more, it will last for generations!
If you’re starting with a new molcajete, it’s worth curing it before using it for the first time. Grinding up some uncooked rice with a splash of water should dislodge any potential grit or sediment from the surface of the mortar. If you see substantial grit in the rice mixture then rinse it out and do it again.
Rinse and de-stem the tomatoes. Roast the tomatoes in the oven at 400ºF for 20 minutes or so.
Finely chop the onion, jalapeño and garlic clove. Add these ingredients to the molcajete along with a pinch of salt. Use the pestle to grind the ingredients together.
Once roasted, add the tomatoes to the molcajete and combine well with the other ingredients. Salt to taste.
Serve immediately and store leftovers in an airtight container in the fridge.
The first time you make homemade salsa, I typically recommend adding the heat (jalapeño pepper) incrementally. I would recommend that for this Salsa de Molcajete as well, so if you want a milder version, you can consider starting with only 1/4 jalapeño.
I use the oven, but you can roast the tomatoes any way you see fit. I typically do not roast the other ingredients, but you can't really go wrong experimenting with that.