Melt some butter over medium-high heat In a large saucepan on the stove.
Add mushrooms and cook until soft, about 5 minutes.
Add in flour and stir until it's all in a paste.Pour in chicken broth and milk and bring to a boil. Reduce heat to low andsimmer until sauce is thickened, about 3 minutes.
In a small mixing bowl, whisk egg yolks withheavy cream. Working quickly, slowly pour in 1/2 cup of the hot mixture iinto theegg mixture while whisking vigorously. Immediately pour this mixture back into the saucepan, whisking the entire time. Cook 2 minutes more.
Stir in frozen peas, drained pimientos, andcooked chicken and let heat through, 2 to 3 minutes.
Serve hot over cooked fried rice, or pasta, or toast,or biscuits.