Trim the duck breasts and lightly score the skin side with a sharp knife.
Spread the cracked peppercorns on to the duck breasts, pressing down the pepper into the breasts. Season with salt.
Heat a large pan over a moderate heat, and place the duck breasts in, skin-side down. Let them cook for 5 minutes or until the skin is nicely golden and crisp.
Turn the breasts over, and cook for approximately 4 minutes more.
Remove the duck breasts from the pan, and keep warm.
Pour off the fat, and deglaze the pan with the cognac.
Add the gravy (or stock), stirring well to scrape up the caramelised juices.
Add the cream and simmer to reduce to sauce consistency.
Fry the mushrooms in the olive oil, and half of the butter.
Fry off the spinach in the remaining butter.
Mix the two together.
To serve, spoon the spinach and mushroom mixture on to warmed plates. Slice the duck breasts, and arrange on top of the spinach mixture. Surround with the sauce.