Add crab cakes to skillet and cook until the underside of the crab cakes are golden brown. This takes about 5-8 minutes, but be sure to check each crab cake every minute to be sure none are cooking too fast.
Remove pan from heat. Add 1 piece of sliced butter on top of each crab cake, then place pan in the heated oven on the top rack.
Broil crab cakes for 6-8 minutes or until the tops are browned to desired doneness. Keep a close eye on crab cakes so they don't burn.
Serve crab cakes immediately on a bed of Beurre Blanc sauce (instructions below).
For the Beurre Blanc
In a saucepan over medium heat, bring white wine, white wine vinegar, and shallots to a boil until the liquid is syrupy and is reduced to about 1-2 tbsp (roughly 5 minutes).
Add heavy cream, salt, and white pepper to saucepan and boil for 1 additional minute.
Reduce heat to a simmer and add butter to saucepan a few pieces at a time, whisking constantly, until all butter has been melted. Cook for an additional 1-3 minutes or until desired sauce thickness is reached.
Pour sauce through a sieve to remove shallots.
Pour sauce through a sieve to remove & discard shallots, then transfer finished Beurre Blanc to a serving bowl.