corned beef and cabbage shepherd's pie

Steps

1. 1put corned beef in a pot with onion and celery and sprinkle spice packet over top.
2. 2pour in cold water to cover.
3. 3turn heat to high and bring to a boil.
4. 4skim off and discard any foam if desired.
5. 5once boiling, reduce heat to low, cover, and simmer gently until tender, about 3 1/2 hours.
6. 6an instant-read thermometer inserted into the center should read at least 145 degrees f (63 degrees c).
7. 7carefully remove corned beef to a bowl and let cool.
8. 8taste broth and add salt if needed.
9. 9bring broth to a boil over high heat.
10. 10add cabbage to the boiling broth.
11. 11cook until cabbage just starts to soften and sweeten up, about 5 minutes.
12. 12use a slotted spoon and remove cabbage to a bowl.
13. 13add carrots to the boiling broth.
14. 14cook until carrots start to soften, about 5 minutes.
15. 15use a slotted spoon and remove carrots to a bowl.
16. 16add potatoes to the boiling broth and reduce heat to medium.
17. 17cook until tender, 15 to 20 minutes.
18. 18while the potatoes are cooking, slice the cooled corned beef along the fatty seam to separate into 2 pieces.
19. 19identify the direction of the meat fibers and cut across them (against the grain) to slice into 1/4-inch thick slices, trimming off and discarding any giant pieces of fat.
20. 20set aside.
21. 21preheat the oven to 400 degrees f (200 degrees c).
22. 22butter a 9x15-inch casserole dish.
23. 23use a slotted spoon and remove cooked potatoes to a bowl.
24. 24reserve broth.
25. 25add butter, salt, pepper, cayenne, and milk to the potatoes.
26. 26mix and mash until very smooth.
27. 27toss in 3/4 cup cheddar cheese and mix until incorporated.
28. 28pour cabbage into the prepared casserole dish and press on it until nicely compacted.
29. 29evenly distribute and press carrots over the cabbage.
30. 30place a nice, even layer of corned beef on top, overlapping a bit and distributing the nice fatty pieces evenly until fully covered.
31. 31pour in 1 cup of the reserved broth.
32. 32dollop mashed potatoes over top, then spread into a uniform layer with the back of a spatula.
33. 33switch to a fork and push potatoes to the edge of the dish.
34. 34then drag the fork sideways back and forth over the potatoes to create a texture.
35. 35repeat this texture going top to bottom over the potatoes.
36. 36sprinkle with a little more cheddar.
37. 37bake in the center of the preheated oven until beautifully browned and piping hot, 45 minutes to 1 hour.
38. 38remove from the oven and let rest for 10 minutes.
39. 39meanwhile, warm any remaining broth over medium-low heat.
40. 40cut shepherd's pie into squares and garnish with scallions.
41. 41serve with warmed broth.