Melt the butter in a pot, add the flour and stir into a ball. Add the chicken broth and stir to a boil, making sure to keep it smooth. Let the sauce boil 7-8 minutes.
Combine the egg yolk and cream and whip it into the sauce, bringing it back to boil.
Strain the sauce, season it with salt, pepper, juice and zest of the lemon. The sauce should be creamy and silky smooth.
Rinse the asparagus and cabbage. Pod the peas. Add the vegetables to the sauce and boil for an additional 1-2 minutes.
Heat the patty shells and fill them with the hot fricassee.