Make Vinegar Reduction: Combine chopped shallot, half of the sorrel, white pepper, and vinegar in a small sauté pan. Simmer over low heat until reduced by 80%. Strain and set aside.
Set Up Double Boiler: Fill a saucepan with 2 inches of water. Bring to a gentle simmer.
Start the Sauce: In a metal bowl, whisk together egg yolks, water, and lemon juice.
Cook the Eggs: Place the bowl over the saucepan (make sure it doesn’t touch the water) and whisk constantly for 2 minutes until thickened slightly.
Add Butter: Whisk in butter one cube at a time, ensuring each piece melts and emulsifies before adding the next.
Finish the Sauce: Remove from heat. Stir in the vinegar reduction, chopped fresh sorrel, a pinch of salt, and a dash of hot sauce if desired.