Step 1

Preheat oven to 425 degrees. Remove neck from inside of poussin cavity, and set aside. Rinse inside and outside of poussin, and pat dry.

Step 2

Season each of the poussin cavities with salt and pepper. Fill each of the cavities with 2 onion quarters, 3 prunes, and 1/3 bunch thyme. Tie the poussin's legs together with kitchen twine, and set aside. Strew the bottom of a large roasting pan with the remaining onion quarters and celery.

Step 3

Rub poussin with 2 tablespoons soft butter; season with salt and pepper. Arrange poussin in roasting pan; place in oven. Roast poussin until golden brown and thigh juices run clear when pierced with a fork, about 55 minutes. Transfer to a serving platter.

Step 4

Add brandy and chicken stock to pan; stir with a wooden spoon to scrape up brown bits from bottom of pan. Strain gravy, and discard solids. Season with salt and pepper. Stir in remaining tablespoon butter. Use gravy to glaze poussin, or serve on the side.