Melt 1 Tbsp butter in a large non-stick skillet over medium-high heat. Cook cutlets until golden brown and cooked through, 2 to 3 minuts per side. Season with salt and pepper to taste. Transfer to plate and tent with foil.

Add remaining butter, garlic, onion, mushrooms, and 1/4 tsp salt to skillet and cook covered until softened, about five minutes. Remove lid and cook until moisture has evaporated, about 4 minutes. Stir in broth, cream, sage, and any accumulated turkey juices and simmer until thickened, about 5 minutes. Season gravy mixture with salt and pepper.

Place 1 bread slice on each plate. Slice cutlets thin and arrange on bread. Top with gravy mixture and serve.