Bring a large pot of salted water to a rolling boil. Add trimmed green and wax beans and cook for 3-4 minutes until beans bend without snapping but still hold their shape. Drain immediately and transfer beans to a bowl of ice water for 2-3 minutes to stop the cooking.
1 lb green beans, 1 lb wax beans
Remove blanched beans from ice water and drain in a colander for 2 minutes. Pat dry thoroughly with a clean kitchen towel to remove excess water that dilutes the dressing.
1 lb green beans, 1 lb wax beans
Slice red onion into thin rounds about ⅛ inch thick. Place the slices in a bowl of cold water and soak for 10 minutes to mellow the sharp bite, then drain and pat dry.
1 small red onion
In a small bowl, whisk vinegar and sugar together until sugar dissolves completely (about 30-60 seconds). Whisk in oil, salt, pepper, and celery seed until dressing is smooth and emulsified.
¾ cup white or apple cider vinegar, ½ cup sugar, ⅓ cup vegetable or olive oil, 1 tsp salt, ½ tsp black pepper, ½ tsp celery seed
In a large bowl, combine blanched beans, drained kidney beans, and prepared sliced onion. Pour dressing over the top and toss gently until everything is evenly coated. Cover and refrigerate for at least 1 hour (up to 12 hours) before serving chilled.
1 lb green beans, 1 lb wax beans, 15 oz kidney beans, 1 small red onion, ¾ cup white or apple cider vinegar, ½ cup sugar, ⅓ cup vegetable or olive oil, 1 tsp salt, ½ tsp black pepper, ½ tsp celery seed
