1. To prepare the radishes: Slice off the tops and bottoms of the radishes, then use a sharp chef’s knife or mandoline to slice the radishes into very thin rounds. Pack the rounds into a pint-sized canning jar. Top with red pepper flakes and mustard seeds.
2. To prepare the brine: In a small saucepan, combine the vinegar, water, honey or maple syrup and salt. Bring the mixture to a boil, stirring occasionally, then pour the mixture over the radishes.
3. Let the mixture cool to room temperature. You can serve the pickles immediately or cover and refrigerate for later consumption. 

Optional add-ins: garlic cloves, black peppercorns, fennel seeds, coriander seeds