Sauté Mushrooms:

In a large saucepan, over medium-high heat, melt 1/2 cup salted butter. Add 8 ounces sliced mushrooms and sauté for about 5 minutes, stirring now and then, until they become tender.

Make Roux Sauce:

Mix in 1/2 cup all-purpose flour and cook for 1-2 minutes, stirring continuously, until no dry flour remains. Slowly add 2 cups chicken broth and 1 1/2 cups milk while stirring. Bring to a boil, then lower the heat to low and let it simmer for around 3 minutes until the sauce thickens.

Temper Egg Mixture:

In a small bowl, combine 2 large egg yolks with 1/3 cup heavy cream and whisk. Gradually whisk in about 1/2 cup of the hot sauce from the pan to temper the eggs (this avoids curdling). Pour the tempered mixture back into the saucepan while whisking constantly. Continue cooking for another 2 minutes to achieve a thicker consistency.

Fold in Chicken and Peas:

Fold in 1 cup frozen peas, 1 (8 ounce jar) drained diced pimientos, and 4 cups shredded cooked chicken. Cook for 2-3 minutes until the peas are hot and the chicken is warmed through. Adjust seasoning with salt and pepper if you like.

Serve Over Rice:

Serve immediately over cooked rice, pasta, toast, or biscuits.