01 - Preheat oven to 350°F. Coat a 9x13-inch baking dish lightly with nonstick spray or butter.
02 - Steam fresh broccoli florets for 3 to 4 minutes until just tender, or if using frozen, thaw and drain thoroughly.
03 - In a skillet over medium heat, melt unsalted butter. Cook chopped onion for 3 to 4 minutes until translucent. Add minced garlic and cook for 1 minute until fragrant.
04 - In a large bowl, mix cooked white rice, steamed broccoli, sautéed onion and garlic, 1 1/2 cups shredded cheddar cheese, sour cream, whole milk, and condensed cream of mushroom soup. Season with salt and black pepper, then stir until well combined.
05 - Spread the mixture evenly into the prepared baking dish. Top with remaining 1/2 cup shredded cheddar cheese. For a crunchy finish, sprinkle breadcrumbs and paprika over the cheese, if desired.
06 - Bake for 30 to 35 minutes, until casserole is bubbly and the top is golden brown. Remove from oven and let cool for 5 minutes before serving.