01 - Melt butter in a large pot or deep skillet over medium heat. Add onions, carrots, and celery, sautéing for 4 to 5 minutes until they begin to soften.
02 - Stir in the minced garlic and cook for 1 minute until fragrant.
03 - Sprinkle flour over the vegetables, stirring to coat evenly. Cook for 1 minute to eliminate the raw flour taste.
04 - Slowly whisk in the chicken broth, then pour in the milk. Bring the mixture to a gentle simmer, stirring constantly.
05 - Add orzo pasta, dried thyme, parsley, salt, and black pepper. Stir well, reduce heat to medium-low, and simmer uncovered for 10 to 12 minutes, stirring occasionally to prevent sticking, until the orzo is al dente and the sauce thickens.
06 - Stir in heavy cream, cooked chicken, and frozen peas. Simmer for 3 to 5 additional minutes until the chicken is heated through and the peas are tender. Adjust salt and pepper to taste.
07 - Remove the pot from the heat and let it sit for 2 to 3 minutes so the sauce can thicken further. Garnish with fresh parsley and serve warm.