Start the beurre blanc while the chicken cooks. In a separate small skillet, combine the wine, peppercorns, and chopped shallot. Bring it to a gentle boil over medium heat and let it reduce by half. This should take about 5 minutes. You are concentrating the flavors here.
½ cup dry white wine (Sauvignon Blanc or Pinot Grigio work well), 6 black peppercorns, 1 small shallot, chopped
Once the wine is reduced by half, pour it through a fine mesh strainer into a bowl, discarding the solids. Return the strained liquid to the pan and reduce for another minute.
Add the lemon juice and reduce again until you have about 2 tablespoons of liquid left in the pan. This is your flavor base. It should taste sharp, acidic, and concentrated.
2 tablespoon lemon juice
Finish the sauce off the heat. Remove the pan from the burner completely and let it cool for a minute or two. The pan should be warm, not hot. Add the cold butter one piece at a time, whisking constantly. Each piece should emulsify into the liquid before you add the next. If the sauce starts to look greasy or separated, your pan is too hot. If it is not coming together, put the pan back on low heat for 20 to 30 seconds while whisking, then pull it off again. Once all the butter is in and the sauce is glossy and thick, you are done.
8 tbs (¼lb) cold unsalted butter - cut in 8-10 pieces