Toast the pasilla chile in a small skillet over medium heat 2 to 4 minutes, flattening it with a spatula occasionally and turning it once or twice. (Do not burn.) Place chile in a small bowl, and cover with about 1 cup of very hot water. Let chile stand 30 minutes or until softened. Drain, reserving water, and set aside.
Cut tomatoes in half crosswise and place, cut-sides up, in a rimmed pan. Add garlic, and drizzle with about 1 tablespoon oil.
Broil about 8 inches from heat 10 to 15 minutes or until tops of tomatoes are slightly blackened. Let cool.
Squeeze pulp from garlic cloves into a blender. Add pasilla chile, tomatoes, and juices from the pan. Add cilantro, salt, and sugar. Blend until smooth. If sauce is too thick, add a little of the reserved chile water. Season to taste with hot sauce.