In a small saucepan, combine vinegar, vermouth, shallot, thyme, salt, and pepper over medium-high heat. Bring to a boil, and cook for 5 to 6 minutes, stirring occasionally, until mixture is reduced to 2 tablespoons. Cool for 5 minutes. Add egg yolks, whisking until smooth.
Put mixture in the top of a double boiler over simmering water. Cook for 1 to 2 minutes, whisking constantly, or until mixture begins to thicken. Remove from heat, and gradually whisk in butter until melted. Whisk in lemon juice. Serve immediately.
Recipe by Southern Lady Magazine at https://southernladymagazine.com/serve-mom-breakfast-in-bed-this-mothers-day/