Make four incisions in the meat and insert the garlic cloves, halved. Season with salt and pepper.
Pour two tablespoons of olive oil into the bottom of a roasting pan, then add the rosemary and sage. Place the rack of veal on top, splash with the white wine, and roast in a preheated oven at 200°C (400°F) for 1 hour and 30 minutes, basting with hot water if necessary.
Thirty minutes before the end of cooking, discard the sage and rosemary, and add the chopped mushrooms, potatoes, and pumpkin to the pan.
Remove from the oven, transfer the meat and roasted vegetables to a serving platter, and serve.