The recipe was in the newest Everyday Food, June '11. Simple, fast and oh, so good. I've made it three times and each time used a different amount of tomatoes and onions. I think it is one of those recipes where you don't have to be specific on the amount of the ingredients and it will turn out great.
So, just put tomatoes (2-6 medium/large), a cut onion (or 1 1/2) 3 jalapeno peppers and 3-5 garlic cloves, unpeeled, on a baking sheet. Broil for about 6 minutes, rotate veggies and broil for another 6-8 minutes. (I take out the garlic after the first 6 minutes.) Remove from oven and let cool.
Remove the really charred bits (or not) and toss everything into the food processor or blender. (Except for the garlic skins and stems from the jalapenos. You may want to use less of the seeds from the jalapenos depending on how spicy you like it.) Stir in some chopped cilantro and juice from a lime. If you do not have a lime you can use about 2 TBLS white vinegar. (My friend, Kelsey, taught me that trick.)
You won't be sorry.