In a small sauce pan, mix together the shallots, beet, wine, vinegar, and bay leaf. Bring to a boil over high heat and reduce by half (about 10 minutes). Add beef stock and continue to boil until reduced by half.
Whisk in the butter and season generously with salt. Add pepper, stir and turn the heat off. Serve immediately or let cool until you can transfer the sauce to a storage container.
The red wine sauce will keep in the fridge for up to a week or freeze up for up to a month.