A few hours before you begin preparing the meal, set out broccoli out to thaw.
Prepare chicken by rinsing, cutting fat away and cubing (about 1/2 inch cubes) both breasts.
Read directions on bag of yellow rice (each brand varies) for water measurement needed for cooking rice. In boiler pot with water, cook the rice until tender. While that is cooking, then...
Add water and butter in medium size fry pan on a medium-high heat. Add raw chicken cubes, cook until all chicken is completely white. Drain.
Make sure rice is cooked, fluffed and tender. Drain any excess water that might be there. Add in salt and pepper to rice, mix.
Make sure broccoli is thawed (if it's not, you can place it in a bowl, add a little bit of water to the bottom of the bowl, cover, and microwave 5-7 minutes until thawed. This will thaw and steam broccoli.) and all water is drained.
In a medium to large size glass baking pan, smooth a thin layer of rice on the bottom. Then smooth some sour cream on top. Add half of the chicken & broccoli. Then smooth some more rice, more sour cream, and then the remainder of the chicken and broccoli. Finish up by smoothing out the remainder of the rice, and the remainder of the sour cream on top.
Bake in the oven for 30-35 minutes on 350 degrees. (Watch sour cream on top to make sure it does not burn in oven. If it does, reduce heat to 325 degrees or try lowering your oven rack.)
Serve hot with a small green salad. (To cut back on time you can prepare the salad while the casserole is baking in the oven.)