2 rhubarb stalks, sliced on a diagonal
1 cup red wine vinegar
1/2 cup sugar
1 1/2 teaspoons kosher salt, plus more
1 fennel bulb, halved, cored, very thinly sliced
3 celery stalks, thinly sliced on a diagonal, plus celery leaves for serving
Olive oil (for drizzling)
Freshly ground black pepper
A heatproof 1-pint jar
Pack rhubarb into jar. Bring vinegar, sugar, 1 1/2 tsp. kosher salt, and 3/4 cup water to a boil in a small saucepan, stirring to dissolve sugar and salt. Pour into jar. Cover and chill until cold, at least 1 hour.
Toss fennel, celery, 1 cup drained pickled rhubarb, and 2 Tbsp. pickling liquid in a large bowl to combine; season with salt.
Arrange salad on a platter; drizzle with oil and grind some pepper over. Top with celery leaves and remaining drained pickled rhubarb.
Do Ahead: Rhubarb can be pickled 1 week ahead. Keep chilled.
– Bon Appetit