Add the potatoes to a large saucepan of salted water. Bring to the boil and cook for 15 to 20 minutes, until very tender.
In a separate saucepan, boil the carrots for 8 to 10 minutes. Add the tenderstem broccoli for the final 3 to 4 minutes, until just tender. Drain and set aside.
Cook the sausages:
Air fryer: Cook until browned and cooked through, turning or shaking halfway. Use the timings and temperature on the sausage packet as a guide.
Oven: Preheat the oven to 200℃ (180℃ fan)/400F (350F fan). Bake sausages on a tray for 20 to 25 minutes, turning halfway, until browned and cooked through.
Drain the potatoes well, return to the pan, then mash with the milk and butter until smooth. Season the mash with salt and black pepper to taste.
Make the gravy by whisking the Bisto granules with boiling water according to the package instructions, then simmer briefly in a small saucepan, stirring, until thickened.
Serve the mashed potato topped with sausages and gravy, with carrots and tenderstem broccoli on the side and enjoy!