Begin by melting the butter in a wide frying pan or a heavy-based casserole dish over medium heat. Add the sliced mushrooms, garlic, and thyme. Sauté for about 4 minutes, stirring occasionally, until the mushrooms soften and take on a golden edge.
Sprinkle the flour over the mushroom mixture and stir well to coat. Let it cook for 1 minute to eliminate any raw taste, forming the base of your sauce.
Pour in the white wine and let it bubble vigorously for around 2 minutes, reducing slightly and lifting any caramelized bits from the bottom of the pan.
Next, add the chicken stock and bring everything to a gentle boil. Once bubbling, lower the heat and allow the mixture to simmer for 5 minutes, reducing slightly and thickening into a flavorful sauce.
Stir in the double cream and toss in the frozen peas. Let it all simmer gently for another 5 minutes, allowing the peas to cook through and the sauce to become rich and velvety.
Finally, fold in the cooked turkey cubes and continue cooking for 2–3 minutes, just until the meat is thoroughly warmed without drying out. Season with salt and pepper to taste.
Serve the fricassee garnished with chopped parsley and a generous sprinkle of grated parmesan if desired. Best enjoyed with crusty bread, mashed potatoes, or rice.