Step 1

Position a wire rack on the top level of the oven, about 6 inches from the broiler. Preheat broiler on high.

Step 2

On a cookie sheet, place onion slices and tomatoes cut side down. Roast until a bit charred on the edges, about 10 minutes.

Step 3

Over medium heat, sauté garlic in 1 tablespoon of vegetable, turning several times with tongs, about 1 minute. Add chiles to garlic, sauté for 1-2 minutes, flipping occasionally until they just start to toast. Take care not to burn.

Step 4

Transfer chiles and garlic to a high-speed blender. Pour in the water and vinegar, and let stand for 5 minutes to soften.

Step 5

Purée on high, 10 to 20 seconds. Turn to low speed and slowly add remaining vegetable oil in a slow and steady stream so the oil mixture will emulsify, creating desired creamy consistency.

Step 6

Add the tomatoes, onion and salt. Purée on high, until smooth.

Step 7

Serve now or store in the fridge for about 2 weeks. Enjoy!