Heat 1 tablespoon olive oil in a skillet over medium heat. Add garlic and cook until sizzling, about 30 seconds. Stir in spinach leaves; cover skillet. Reduce heat to low and cook until spinach is just wilted, stirring occasionally, 4 to 5 minutes.
Mix flour, salt, and pepper together in a shallow bowl. Press each cutlet into flour mixture to coat; shake off excess flour. Place the floured cutlets onto a plate while flouring the rest; do not stack. Place 2 sage leaves and 1 prosciutto slice on each floured cutlet, roll cutlets, and secure with toothpicks at each end. Refrigerate cutlet rolls for 30 minutes.
Heat remaining olive oil in a skillet over medium heat. Cook cutlet rolls until veal is browned but still slightly pink in the center, 1 to 2 minutes per side. An instant-read thermometer inserted into the center should read 145 degrees F (63 degrees C). Place cooked cutlets in a baking dish and place in preheated oven to keep warm.
Pour Marsala wine into the skillet and bring to a boil while scraping the browned bits of food from the bottom of the skillet with a wooden spoon. Stir in butter until smooth, 1 to 2 minutes.
Place spinach on a large serving platter. Place cutlets on top of spinach, pour Marsala Wine mixture over the cutlets, and top with hard-boiled egg slices to serve.