Bring a steamer pot of water to a boil. Peel the potato and cut it into large chunks. Roughly chop the spinach. Cook potato in the steamer pot of boiling water until tender, 10-15 mins. When there are 2 mins cooking time remaining, add the spinach and toss through. Once cooked, transfer the potato and spinach to a large bowl. Reserve the steamer pot with water. Add oil, milk, a generous pinch of salt and garlic aioli, then mash until smooth. Cover to keep warm.
Cook veggies
Trim broccoli and slice lengthways in half. Remove the husk from the corn cobs and slice in half. Bring the reserved steamer pot back to a boil, and top up with water if needed. Cook the corn and broccoli for 4-5 mins, until tender. Set aside with the lid on to keep warm.
Cook beef
Meanwhile, heat the oil in a large frypan over high heat. Season beef with salt and pepper and add to hot frypan. Cook for 2-3 min on each side, or until cooked to your liking. Remove from heat and rest for 4 mins.
Make sauce
While the steak is resting, peel and mince the garlic. Heat the oil in a small pot. Add freshly ground pepper and garlic and cook until fragrant, 1 min. Reduce heat to medium, add coconut cream and crumble in the beef stock cube and cook until thickened, 1-2 mins. Stir through any steak resting juices and slice the steak. Season with salt and pepper.
To serve
Divide the seared beef sirloin, spinach and potato mash, corn and broccoli between plates. Pour over the creamy peppercorn sauce.