The flavors in this simple salad get better as the beans marinate and soak up the dressing.
Soak onion in cold water, 10 minutes.
Meanwhile, whisk Dijon and vinegar in a bowl. Slowly whisk in oil until combined. Drain onion and dry well. Stir into dressing along with beans and herbs; season with salt and pepper. Let sit 15 to 20 minutes or refrigerate in an airtight container up to 5 days. Serve as a side, over meat and fish, on toasted rustic bread, or mixed into greens.
This recipe can be made with any kind of beans. You can also use a 15.5-ounce can instead of homemade -- just drain and rinse first.