Heat butter over medium heat in a large skillet.
Add shallot and mushrooms to butter and sauté for a few minutes until the shallot is translucent and the mushrooms have softened.
Add the minced garlic and sauté another minute until fragrant.
Add flour to the mushroom mixture. Stir to combine and continue to sauté another few minutes until the flour has cooked through
Once flour has cooked through, deglaze the skillet with cooking sherry. Then add chicken stock and half and half slowly, stirring constantly. Heat the mixture and continue stirring until thickened.
Add cooked chicken (use leftover or rotisserie) and pimientos to the mixture. Stir to combine and heat through. Stir in frozen peas.
Adjust seasoning with salt and lots of freshly cracked black pepper to taste. You can add more stock to adjust the thickness, if needed.
Serve piping hot over rice or biscuits. Garnish with freshly chopped parsley. Enjoy!