Bring a pot to heat over medium-high heat, and melt the butter. Stir in the onion and cook until it is slightly opaque. About 2-3 minutes.
Mix in the rice, stock, and cream, then bring to a boil. Reduce heat, cover with a lid, and simmer until all the liquid has been absorbed and the rice has cooked - approximately 15-20 minutes. Remove from heat and set aside.
Heat another pot over medium-high heat and add oil. Mix in corn, broccoli, and salt. Cook until tender - approximately 3-5 minutes.
Spoon the rice mixture into the broccoli, add the cheddar and a ¼ cup of parmesan, and stir to combine.
Combine melted butter, panko, remaining parmesan, and smoked paprika in a bowl. Stir to incorporate.
Spoon your broccoli and rice mixture evenly into a greased casserole dish and top with breadcrumb mix.
Cook at 350F for 25-30 minutes, - when the panko topping is golden brown. Once out of the oven, allow the casserole 5-10 minutes to cool.
Cut into individual portions, serve, and enjoy!
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Notes
Cooking times may vary depending on the size of the casserole dish, your oven, etc. Keep an eye on your broccoli rice casserole in the oven to avoid overcooking and drying it out.