Melt butter in a saucepan over medium heat. Add sliced mushrooms and cook until soft.
Sprinkle in flour, stirring until combined with the butter and liquid from the mushrooms.
Pour in chicken broth and milk, bring to a simmer to thicken the sauce.
Whisk together egg yolks and heavy cream in a small bowl.
Temper the yolks by adding a ladle of the thickened mixture, then pour back into the sauce.
Cook over low heat for 2 minutes, then add peas, pimentos, and cooked chicken.
Stir and cook for a few more minutes until heated through.
Serve over rice, toast, biscuits, or pasta. Enjoy!
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