- Sweat the shallots in butter in a small saucepan over medium heat for 3 to 4 minutes while stirring. Add duck stock, reduce by half or until smooth, and add balsamic vinegar at the end of cooking. Season with pepper, but taste before adding salt because stock is highly seasoned when reduced. Set aside.
- Preheat oven to 200°C (400°F). Coat grapes in olive oil and place them on a parchment-lined baking sheet. Season with salt and pepper. Bake in oven for 10 to 15 minutes, stirring once. Set aside.
- Use a knife point to make a criss-cross pattern in the breast fat without touching the meat. Generously season both sides of the breasts with salt. Fry in a dry skillet over medium-high heat, skin-side down, until fat is golden brown and crispy. Turn breasts over, reduce heat to medium, and continue frying. Breast meat is best when slightly pink. Spoon off excess fat while cooking. Covered and wait 5 minutes before carving.
- In the meantime, cook celeriac, potato, and garlic in a saucepan of boiling water for 15 to 20 minutes, or until vegetables are tender.
- Drain vegetables and return them to saucepan to dry, shaking the pan over the lit burner. Using a hand masher, purée the vegetables and add enough cream and butter. Season with salt and pepper.
- Immediately before serving, cut duck into thin slices. Overlap some slices on a plate. Drizzle with sauce and garnish with roasted grapes. Serve with mashed potatoes and celeriac.
Roasted grapes are also delicious for garnishing sausages, pork, or chicken.
Leftover sliced duck? Use it in a salad or in a sandwich topped with chutney.