Remove the husks from the tomatillos and wash them well, then chop them into bite-sized chunks.
Mince 1/2 cup red onion, 2 cloves garlic, and 1/2 jalapeño pepper, taking proper care to wash your hands after handling the pepper. Chop 1/2 cup cilantro.
Mix all ingredients together in a bowl and add the juice of 1 lime, 1 teaspoon sugar, and a few pinches kosher salt. Taste and adjust seasoning as desired. Serve with tortilla chips, in a burrito, or as an accompaniment to chicken or fish.