Make white sauce: Melt butter over low heat. Remove from heat and stir in flour. Add milk and return to heat. Stir until thick and smooth. Remove from heat and stir in lemon juice, mustard, salt, pepper and worcestershire sauce.
Stir in unbeaten eggs yolks. Put crabmeat in a greased 8 x 8" casserole dish; add white sauce and gently stir in crabmeat.
Put breadcrumbs and Parmesan cheese on top of casserole. Bake in 375 degrees F oven until bubbly or browned a little--approximately 1/2 hour to 45 minutes, depending on oven.