chopped chives (for serving)
1/2 cup heavy cream
3/4 cup buttermilk
1/4 tsp. baking soda
2 tsp. baking powder
1 1/2 cups all-purpose flour, divided
ground black pepper
1/2 cup chicken fat (schmaltz) or butter
kosher salt
2 tsp. whole peppercorns
1 bay leaf
1/2 bunch parsley stems
4 sprigs thyme
3 cloves garlic
1 medium onion, chopped, divided
4 stalks celery
4 carrots
1 leek, pale-green and white parts only
4 chicken legs