Ingredients

• 1/2 teaspoon fennel seeds
• 1/4 teaspoon black or brown mustard seeds
• 1 medium tomato, halved crosswise, seeds removed
• 5 fresh red chiles (such as Fresno)
• 2 tablespoons distilled white vinegar
• 1 teaspoon Kashmiri chili powder or paprika
• 1 teaspoon kosher salt
• 1/2 teaspoon sugar
• A spice mill or mortar and pestle

Instructions

1. Toast fennel seeds and mustard seeds in a dry small saucepan over medium heat, shaking pan often, until fragrant, about 45 seconds. Transfer to a plate and let cool. Finely grind in spice mill or with mortar and pestle. Transfer back to pan.
2. Pulse tomato and chiles in a food processor until finely ground. Transfer to saucepan with ground spices and mix in vinegar, chili powder, salt, and sugar. Bring to a simmer over medium heat, stirring often; cook until chiles are soft and sauce is slightly thickened, 5–7 minutes. Let cool.
3. Hot sauce can be made 1 week ahead. Cover and chill.