Toss this sauce with noodles, or serve as a dip for grilled tofu or tempeh skewers or fresh vegetables—you can even thin it with water for a salad dressing. For more authentic Indonesian flavor, substitute kecap manis, a thick, sweet Indonesian soy sauce, for the soy sauce and reduce the brown sugar to 1 teaspoon. The sauce will keep up to a week in the fridge.
Heat oil in saucepan over medium-low heat. Sauté shallot in oil 2 minutes, or until beginning to soften. Add garlic and red pepper flakes, and sauté 1 minute more, or until just fragrant. Whisk in peanut butter, coconut milk, soy sauce, brown sugar, and 1/2 cup water until smooth, and bring to a boil. Reduce heat to medium-low, and simmer 5 minutes. Stir in lime juice. Serve hot, or at room temperature.