- Heat oven to 190c or Gas 5.
- Open the tin of corned beef, slice and lay in the bottom of a buttered, medium oven-safe dish.
- Gently cook the sliced onions in a pan with the oil and butter until soft but not brown. Lay them on top of the corned beef.
- Open the tin of beans and pour onto the meat and onions. At this point you could add a sprinkling of chilli flakes, if liked.
- Cover the whole mixture with the mashed potato spreading with a fork to make lines across the top which will brown nicely in the oven.
- Pop the dish in the oven and heat through. When the potato is golden and crunchy, remove from the oven and tuck in!