Place the grouse breasts on a chopping board, leaving a little space between them. Cover them with clingfilm and gently pound them out using your fists or a rolling pin until they are about ¼” thick.
Season each breast with pepper. There’s no need for salt since the prosciutto is quite salty already.
Take a slice of prosciutto and press it onto each breast. Fold any excess onto itself and make sure it sticks to the breast.
Lightly dredge each piece in the flour and shake off the excess.
In a saucepan, heat 2 tablespoons of olive oil over medium-high heat. Once hot, add the 10 sage leaves and cook until crispy. Be careful not to burn them. Once they’re crispy, remove them from the pan and set them aside.
In the same pan, add 2 tablespoons of unsalted butter over medium-high heat. Add 2 breasts, prosciutto side down, and fry them for two minutes until the prosciutto is crispy. Then, turn them over and fry the breasts for another two minutes until golden brown. Set them aside on a plate and cover them with foil. Do the same with the other two, adding more butter if needed. Set them aside with the other 2 breasts on the covered plate.
Deglaze the pan with the wine, scraping up the brown bits in the pan. Then, reduce the sauce by half. Remove the pan from the heat and add the remaining butter one tablespoon at a time. Whisk until the butter is incorporated and has a glossy look. Break up some of the crispy sage leaves and add them in, too.
Place each grouse breast on a warm plate and pour sauce over each breast. Garnish with the remaining crispy sage leaves.
Serve with your choice of sides. I recommend roasted potatoes, sautéed greens like Swiss chard, and good crusty bread to help you mop up the sauce left on your plate.