My recipes involve a lot of eyeing and guesswork, so you’ll want to take these amounts as suggestions rather than absolutes.

Reuben soup:

8-10 oz of corned beef
small amount of butter or oil
1 small onion
1 cup well-drained sauerkraut
3 cups beef stock
8-16 oz swiss cheese, shredded

either:
8 oz brick of cream cheese or
roux

Saute the corned beef and onion in the butter/oil in the bottom of a saucepan. You just want to release some of the great flavors in the onion. Add the stock and the sauerkraut. Simmer for 10-20 minutes until the flavors blend. Turn down heat. Stir in the swiss cheese until melted. Thicken with some cream cheese or roux. Can be topped like french onion soup with a slice of rye bread and some swiss.