Preheat your oven to Combi Steam, 400°F/200°C, 50% (medium) steam.
Put half of the butter in a large baking dish and scatter the chopped onions over the top. Place in the oven and cook for 10-15 minutes, stirring a few times, until the onions are soft and turning golden. Add the garlic and spices and return the dish to the oven for 2 minutes.
4 Tbsp butter, 1 onion, 2 cloves garlic, 2 tsp garam masala, 1 tsp turmeric, 1/2 tsp mustard seeds
Add the potatoes to the dish, mixing to coat them in the aromatics and spices. Put the dish back in the oven and cook for 10 minutes, then toss the potatoes around, crushing them slightly with the back of the spoon. Add the rest of the butter at this point if it’s looking a little dry.
4 Tbsp butter, 1 lb steamed potatoes
Return to the oven again and continue cooking for a further 10-15 minutes, until the potatoes are very soft and and beginning to brown at the edges. The onions and garlic should be golden.
Season everything well with salt and pepper and serve warm, making sure you scrape any golden crusty bits from the dish as you’re serving up. Scatter the red and green onions over the top.
Salt and black pepper, Sliced red onion and green onion to serve