Preheat oven to 350ºF. Lightly spray a 9×9-inch pan with cooking spray and set aside.: The room will warm and a faint scent of heat will fill the kitchen as the oven reaches 350ºF , signaling that this dish will transform from mixed ingredients to a cohesive casserole. Preheating ensures even baking so the center firms up at the same rate the topping browns. A common mistake is placing the dish in a cold oven, which can lead to a soggy center and uneven browning. Make sure the pan is at room temperature, and lightly spraying prevents sticking while preserving the buttery topping texture.
In a bowl, combine rice, broccoli, corn, egg, onion powder, garlic powder, salt and pepper. Pour mixture into pan.: Immediately after combining, you will notice a mix of textures and colors, the pale grains of rice interspersed with little green flecks of broccoli and kernels of creamy corn . The beaten egg spreads through the mixture and gives a slightly glossy finish, which will help everything hold together. Smell the gentle aromatics of onion powder and garlic powder as they bloom into the wet ingredients, enhancing savory notes. Stir thoroughly so the seasonings distribute evenly; failing to mix well can lead to pockets that are over salted or under seasoned.
Toss crackers with melted butter. Sprinkle over broccoli mixture.: When you toss the crushed crackers with warm melted butter , the crumbs clump slightly and take on a shiny, fragrant coating. As you sprinkle them over the top, you will see an even layer that will crisp during baking. That sizzling crunch develops as the butter browns and the cracker edges toast, adding a toasty aroma to the kitchen. If the cracker layer is applied too thickly, the top can burn before the center sets, so aim for an even, moderate coverage to achieve that balanced golden finish.
Bake uncovered for 25 to 30 minutes.: During the baking time, steam will escape and the interior will bubble gently, while the cracker topping turns a warm golden color. You should notice small bubbling around the edges, and a slight jiggle in the center when you gently shake the pan, indicating the casserole is nearly set. The scent will deepen from mild to toasty, and the top will gain color. A common error is overbaking, which can dry the casserole and make the rice grainy; remove it when the center barely jiggles and the topping is nicely browned.