Melt butter in a saucepan over a medium heat. Add flour. Cook stirring, for 1 minute. Gradually stir in milk and increase heat to medium. Cook constantly stirring until the sauce coat t he back of a wooden spoon. Stir in parsley, lemon juice and lemon zest and remove from heat. Season with salt.
Season salmon with salt and white pepper. Place olive oil in a hot skillet then put the Salmon in the skillet (skin side up). Sear salmon for in hot skillet for 2-3 minutes on each side or until salmon is just cooked through.
Place the half the sauce on the plate then the salmon on top of the sauce. Garnish as desired.