Preheat oven to 375 degrees F (190 degrees C). Lightly grease a medium baking dish.
Arrange salmon in the prepared baking dish. Evenly coat with sour cream. Season with white pepper and dill.
Bake in the preheated oven 30 minutes, or until fish is easily flaked with a fork.
In a small saucepan over medium heat, mix the wine and shallot, and bring to a boil. Reduce heat, and simmer 10 minutes, until liquid is reduced by about 2 tablespoons.
In a small bowl, thoroughly blend the half-and-half and flour, and stir into the wine mixture. Return the mixture to a boil, stirring constantly. Reduce heat, and continue to cook and stir until thickened.
Remove the wine and cream mixture from heat, and mix in the Dijon mustard. Pour evenly over the salmon to serve.