Bring a medium saucepan of lightly salted water to the boil. Peel the potato and cut into large chunks. Finely chop the brown onion and garlic. Grate the celery and carrot. Trim the green beans then slice in half.

Cook the potato in the boiling water until easily pierced with a knife, 12-15 minutes. Drain and return to the pan. Add the butter, milk and the salt. Mash until smooth. Stir through the shredded Cheddar cheese 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. Cook the onion, celery, carrot, green beans and a generous pinch of salt, stirring, until softened, 4-5 minutes. Transfer the veggies to a bowl. Return the pan to a high heat with another drizzle of olive oil. When the oil is hot, cook the beef mince and garlic, breaking up the mince with a spoon, until just browned, 2-3 minutes. TIP: Transferring the veggies out of the pan allows the beef to brown! TIP: For best results, drain the oil from the pan at the end of of this step!

Add the tomato paste, the water and beef stock pot. Stir to combine, then return the veggies to the pan. TIP: Add a dash of water at the end if the filling seems too thick!

Preheat the grill to medium-high. Transfer the filling to a baking dish. Spread the Cheddar mash on top. Grill until lightly golden, 5-7 minutes.

Slice the beef & veggie cottage pie. Divide between plates to serve.