Place 1 ½ pounds boneless, skinless chicken breasts on cutting board. Trim chicken as needed, then cut chicken breasts into bite-sized pieces.
Season chicken on all sides with generous amounts of salt and freshly cracked black pepper.
Place large skillet on stovetop over medium-high heat. Add 1 tablespoon neutral-flavored oil to pan. Heat pan until oil is hot and shimmery.
When oil is hot, add seasoned chicken pieces to skillet. Sear chicken pieces, flipping chicken over as needed, until lightly browned on all sides. Transfer seared chicken to large bowl and set aside.
Return skillet to heat. Add 4 tablespoons unsalted butter to skillet and let butter melt completely.
Once butter has melted, add 1 cup chopped white onion and 1 ½ tablespoons minced fresh garlic to pan. Stir to incorporate. Sauté ingredients, stirring occasionally, 5 minutes or until onions are translucent.
When onions are translucent, add 1 ½ cups long-grain white rice to skillet. Stir to incorporate, then toast rice 2 to 3 minutes, stirring frequently.
Once rice is toasted, add 3 cups chicken broth and stir to incorporate. Allow liquid to begin to simmer.
Return chicken to skillet now if desired (see Notes). Stir to incorporate, then place lid on skillet and reduce heat under pan to low. Simmer chicken and rice 20 minutes or until rice is tender. Note: Check rice periodically. If all liquid is absorbed before rice is tender, stir in 1 additional cup chicken broth.
Once rice is tender, remove skillet from heat and let mixture cool slightly.
Add 1 cup heavy cream, 1 tablespoon lemon juice, 1 ½ teaspoons salt, and freshly cracked black pepper. Stir until incorporated.
Add 1 cup shredded fresh parmesan to pan. Stir until cheese is incorporated, then return skillet to heat. Continue stirring mixture until parmesan is melted and sauce is warmed through.
Portion chicken and rice mixture into serving bowls. Garnish with chopped fresh parsley if desired and serve warm.