Place the potatoes in a microwave safe bowl, microwave for 10 minutes, then allow to cool.
Preheat the oven to 180˚C fan-forced (200˚C conventional).
Roughly chop the potatoes, then add to a large baking dish with the onion and skin-on garlic cloves.
Roughly chop the sausages and nestle them around the potatoes.
Drizzle with the oil, then bake for 30 minutes.
Meanwhile, melt the butter in a small saucepan over medium heat, then whisk in the flour.
Gradually add the milk, stirring well between additions, to create a smooth béchamel sauce.
Stir through the vegetable stock powder.
Remove the baking dish from the oven and squeeze the roasted garlic out from its skins.
Add the frozen peas to the tray, season very well with salt, then pour the béchamel sauce over everything.
Sprinkle with the shredded cheese, then bake for a further 20 minutes, or until golden-brown.
