Bring a pot of water to a boil, then cook the broccoli until it has just begun to turn tender. Cool it immediately in an ice bath or under cold running water so the florets stop cooking and keep their shape.

Drain the chilled broccoli well and set it aside. Pat the florets dry so they feel free of surface water before they meet the cheese sauce.

Heat the oven to 375 °F. Prepare for a hot oven that will bake the filling until it bubbles around the edges.

Melt the butter in a pot over medium heat. It should melt gently without browning before the onion goes in.

Cook the chopped onion in the butter until softened. Look for translucent pieces and a mellow, savory aroma.

Stir in the minced garlic and cook for 30 seconds. The garlic should smell fragrant without taking on color.

Add the softened cream cheese and stir until it melts completely. Keep stirring until no firm white pieces remain in the pot.

Whisk in the heavy whipping cream slowly. The mixture should become smooth, glossy, and evenly blended.

Stir in the cheddar cheese and colby jack cheese until melted. Use gentle heat and stop when the sauce looks uniform and velvety rather than oily.

Place the broccoli in a large mixing bowl and pour the cheese sauce over it. Fold gently until each floret is coated without breaking it apart.

Transfer the broccoli mixture to a well-greased 9x9 baking dish. Spread it into an even layer so the casserole bakes evenly.

Mix the pork rind crumbs and Parmesan cheese in a bowl. The topping should look evenly combined, with Parmesan distributed through the crumbs.

Scatter the crumb mixture over the casserole. Cover the surface evenly for a crisp bite in every serving.

Bake for 25 minutes. The casserole is ready when the edges bubble gently and the topping is lightly browned.