Blanch the bell peppers in briskly boiling water for about five minutes or until the skins blister. Scoop out, cool a bit and peel off the skins. Cut off the stems, slit and scoop out the seeds.
In a small sauce pan, heat the vinegar and garlic.
Place the bell peppers, vinegar and garlic in a food processor. Process on high speed until pureed.
With the motor running, pour the olive oil in the thin stream through the spout. The sauce will lighten in color as the mixture emulsifies.
Pour the sauce into a bowl. Add salt to taste.