Ingredients

• 2 (12-ounce) bags frozen pearl onions, thawed
• 2 tablespoons coriander seeds
• 1 tablespoon fennel seeds
• 2 teaspoons whole black peppercorns
• 1 whole dried chile de árbol or 1/2 teaspoon red pepper flakes
• 5 sprigs thyme
• 2 2/3 cups red wine vinegar
• 1 1/3 cups sugar

Instructions

1. Bring a large saucepan of heavily salted water to a boil. Add onions and cook until crisp-tender, about 4 minutes. Drain and transfer to a large heatproof bowl.
2. Cook coriander seeds, fennel seeds, and peppercorns in another large saucepan over medium heat, stirring occasionally, until lightly toasted, about 2 minutes. Add chile, thyme, vinegar, and sugar; bring to a boil, stirring until sugar dissolves. Remove from heat; add to bowl with onions. Let cool to room temperature, then cover and chill at least 12 hours before serving.