Chicken and Biscuits

Add carrots, celery root, onion, and leek; stir frequently until softened and beginning to brown, 8-10 minutes.

Add butter; stir until melted.

Add flour and stir constantly until well blended, about 2 minutes.

Add wine and 1/2 cup water.

Bring to a boil; reduce heat and simmer until liquid is reduced by half, 5-8 minutes.

Add chicken, broth, thyme, rosemary, and bay leaves.

Bring to a boil; reduce heat.

Simmer until chicken is fork-tender, 35-40 minutes.

Transfer chicken to a plate.

Let cool slightly; shred meat, discarding skin and bones.

Return shredded chicken to soup.

Add 1 1/2 teaspoons vinegar.

Season with salt, pepper, and more vinegar, if desired.

DO AHEAD: Soup can be made 2 days ahead.

Let cool slightly; chill until cold.

Cover and keep chilled.

Reheat before serving.

Whisk flour, salt, and baking powder in a large bowl.

Using your fingertips, blend until pea-size lumps form.

Add buttermilk, crème fraîche, and chives.

Using a fork, mix until just combined.

Gather mixture into a ball and knead in bowl just until a shaggy dough forms, 3 or 4 times.

Transfer dough to a floured work surface and pat into a 3/4"- to 1"-thick round.

Cut out rounds with a 2" biscuit cutter or small glass.

Gather dough and repeat patting and cutting.

Transfer to a parchment-lined rimmed baking sheet; brush with egg.

Bake biscuits until golden brown, 25-30 minutes.

Serve warm or at room temperature.

DO AHEAD: Biscuits can be made 8 hours ahead.

Let cool completely and store airtight at room temperature.

Divide soup among bowls and top with biscuits.