How to Make It
Pack the chiles and garlic in a 1-quart heatproof jar.
In a small saucepan, toast the mustard seeds, coriander seeds, fennel seeds and peppercorns over low heat, stirring, until very fragrant, about 3 minutes. Add the vinegar, sugar, salt and 1 cup of water and bring to a simmer. Cook for 5 minutes, stirring to dissolve the sugar and salt. Pour the hot brine over the chiles and garlic and let cool to room temperature, about 2 hours. Serve immediately or refrigerate in the brine.