How to Make It
Bring water, sugar, 1/2 cup vinegar, and 1 1/2 teaspoons salt to a boil in a small saucepan over high. Boil, whisking until sugar and salt dissolve, about 1 minute. Remove from heat.
Place onions and beets in a glass bowl; add vinegar mixture. Let stand at room temperature 1 hour. Drain and serve, or chill up to 2 weeks.
Whisk together buttermilk, mayonnaise, and olive oil in a bowl until smooth. Whisk in parsley, chives, garlic, and remaining 1 tablespoon vinegar. Stir in pepper and remaining 3/4 teaspoon salt.
Toss together kale, onion mixture, and 1/2 cup dressing. Top with eggs, parsley, chives, and croutons. Serve with remaining dressing.