Bring a medium saucepan of lightly salted water to the boil. Peel the potato and cut into large chunks. Roughly chop the parsley. Finely chop the brown onion and garlic. Grate the celery and carrot.

Cook the potato in the boiling water until easily pierced with a knife, 10-15 minutes. Drain and return to the saucepan. Add the butter, milk and the salt, then mash with a potato masher or fork until smooth. Stir through the shredded Cheddar cheese and parsley until well combined. Cover to keep warm.

While the potato is cooking, heat a drizzle of olive oil in a large frying pan over a high heat. Add the onion, celery, carrot and a generous pinch of salt and cook, stirring, until softened, 4-5 minutes. Transfer the veggies to a bowl. Return the pan to a high heat with a drizzle of olive oil. Cook the garlic and beef mince, breaking up with a spoon, until just browned, 2-3 minutes. TIP: Transferring the veggies out of the pan allows the beef to brown!

Add the tomato paste and the water to the frying pan and add in the beef stock pot. Return the veggies to the pan. Stir to combine. Add the baby spinach leaves and stir through until just wilted, 1 minute. Stir in a dash of water if the filling is very thick.

Preheat the grill to medium-high. Transfer the filling to a baking dish and spread the mash on top. Grill until lightly golden, 5-7 minutes. TIP: Keep an eye on the mash topping as it can burn quickly!

Divide the beef cottage pie between bowls.