Preheat and Prep: Start by preheating your oven to 350°F (175°C). Lightly grease a 9x13-inch baking dish with butter or non-stick spray to ensure easy serving later.
Mix the Pineapple Base: In a large mixing bowl, toss the drained pineapple chunks with the sugar and flour. Stir until the pineapple is evenly coated and the flour has completely dissolved—this creates that lovely, slightly thickened sauce as it bakes.
Add the Sharpness: Fold in the freshly grated cheddar cheese. Mix until the cheese is distributed evenly throughout the pineapple.
Transfer: Pour the mixture into your prepared baking dish, spreading it out into an even layer.
Create the Golden Topping: In a separate small bowl, combine your crushed crackers with the melted butter. Stir until all the crumbs are moistened and look like wet sand.
The Final Layer: Sprinkle the buttery cracker crumbs evenly over the top of the pineapple mixture. Do not press down on the crumbs; keeping them loose ensures they stay light and crispy.
Bake to Perfection: Place the dish in the oven for 30 minutes. You’re looking for a beautiful golden-brown top and a filling that is bubbling around the edges.
Rest and Serve: Let the casserole sit for about 5 to 10 minutes before serving. This allows the sauce to set slightly so it isn't too runny on the plate.