Slice the onions thinly and reduce by simmering in 1.5 oz of butter for 20 to 30 minutes.
Braise the sliced turnips in 1.5 oz of butter. Preheat oven to 350 °F. On each circle of puff pastry, spread the onion compote, add the turnip slices. Bake for 15 to 20 minutes.
Meanwhile, cut the duck breasts into 16 pieces.
Sear the dices of foie gras for 1 minute, constantly stirring for even coloring. In another pan, sear the duck breast pieces for 2 minutes on each side.
Deglaze with poultry stock. Keep the sauce warm.
Skewer each rosemary branch with 4 cubes of duck breast and a few dices of foie gras. Season the baby spinach with balsamic vinegar and olive oil. Season with salt and pepper to taste.
On each plate, arrange the baby spinach salad in the center. Put a skewer in the center and the puff pastry with onion compote and turnips on top; drizzle with sauce. Serve immediately.