Cook the rice.
If using uncooked white rice, simmer it in the chicken broth until tender and fluffy. This adds extra flavor. If using pre-cooked rice, warm it slightly so it’s easier to mix.
Sauté the aromatics.
In a large skillet, heat olive oil over medium heat. Add onion, celery, and a pinch of salt. Cook 5–6 minutes until soft.
Stir in garlic for 30 seconds.
Make a simple cream sauce. Add butter to the skillet and let it melt. Sprinkle in flour and whisk for 1–2 minutes to form a paste.
Slowly pour in milk, whisking constantly. Simmer until thick and smooth, about 3–4 minutes.
Season it right. Stir in paprika, thyme, 1 teaspoon salt, and 1/2 teaspoon pepper.
Taste and adjust. Take the pan off the heat and stir in sour cream and 1 1/2 cups of the cheddar until melted.
Combine the base. In a large bowl, mix the cooked rice, chicken, thawed peas and carrots, and the cream sauce.
Fold gently until everything is coated.
Assemble. Spray a 9x13-inch baking dish (or two 8x8-inch dishes). Spread the mixture evenly.
Top with remaining 1/2 cup cheddar.
Add the crunch. Combine crushed crackers or panko with melted butter. Sprinkle evenly over the top.
To bake now: Cover with foil and bake at 350°F (175°C) for 20 minutes.
Uncover and bake 10–15 minutes more until hot and bubbly with a golden top.
To freeze: Skip baking. Cool completely, wrap tightly in plastic, then foil, and label with the date and baking instructions.