Place the chiles and sun dried tomatoes into 2 separate heat proof bowls. Pour boiling water over them, enough to completely cover. Allow to steep for at least 30 minutes.
Drain the chiles and rinse with cool water. Drain again. Put on rubber or latex gloves, and remove the stems from the chiles using a sharp paring knife. Slit each chile open and gently remove the seeds and membranes. Don't worry if you miss a few - we'll deal with them later. NOTE: Be very careful not to touch your eyes, nose, lips or other sensitive areas while cleaning the chiles - they are very, very hot!
Peel the onion and coarsely slice it into large wedges. Peel the garlic cloves and cut in half. Place on a baking sheet or pan and place under a preheated broiler. Allow to cook for 5 - 10 minutes, or until the tops of the onions and garlic are slightly charred. Watch carefully and do not allow to burn!
Drain the sun dried tomatoes, reserving the liquid.
Place the cleaned chiles, sun dried tomatoes, onion and garlic in a food processor or blender. Pour some of the tomato soaking water in and add a big pinch of sea salt.
Process on high until fairly smooth, adding more liquid as necessary (you want a consistency about the same as ketchup or tomato sauce).
Strain the mixture through a fine mesh sieve, forcing it through with the back of a spoon or ladle. Discard the coarse solids.
Add a little water as necessary to achieve the desired consistency and more salt to taste.
Watch out - this salsa is hot, but addictive! Use it as is, or as a base for other sauces and dishes.