In large bowl, place 1 cup of the potatoes and mash with a fork. Add
the remaining 1 cup potatoes, corned beef, cooking liquid, onion,
garlic, mustard, thyme, and nutmeg. Store in the refrigerator overnight
before cooking or proceed with canning.

To cook:

Heat 1/4 cup butter in a large cast-iron skillet over medium-high
heat. When the foaming subsides, add the hash mixture and cook,
stirring, for 30 seconds. Using a spatula, press the mixture down
into a round cake the size of the skillet. Cook, shaking the skillet
occasionally, for 4 minutes. Reduce the heat to medium and continue
cooking, moving the skillet occasionally, until the underside is
browned and crusty, about 6 minutes more.
To flip the hash, set a plate the size of the skillet on top of the
pan. Invert the pan so the hash falls on to the plate as an intact
cake. Return the skillet to the heat, raise to medium-high, and heat the remaining 1
tablespoon butter. When the foaming subsides, slide the hash into
the skillet cooked-side up. Cook, shaking the skillet occasionally,
for 3 minutes. Reduce the heat to medium and cook, shaking the
skillet occasionally, until the underside is browned and crispy,
about 5 minutes more.

To can:

Pack mixture into pint or smaller jars, leaving 1” headspace.
Process in pressure canner for 75” at 10 lbs. Adjust for altitude.

NOTE: as written, makes a little over 2 pints. Doubled it and got 5 pints

More pics at bottom of this recipe.