Preheat oven to 350 degrees. Spray a medium cooking dish with cooking spray.: The warm scent of the oven and the slight dry heat create an even environment for baking, which is crucial for crisping the topping without overcooking the interior. Make sure the oven reaches the full temperature before you slide the dish in, because inconsistent heat can leave the crumbs pale instead of golden. A common mistake is to skip preheating, which slows the baking and affects the texture. If your oven runs hot, adjust slightly and check the dish midway to prevent over browning.
Steam broccoli florets until firm but tender for about 2-3 minutes. I put my broccoli in a microwave safe bowl with 2 inches of water and microwave it for 3 minutes. Drain well then pat dry with paper towels to remove as much moisture as possible.: You will notice the broccoli brighten to a vivid green and give a gentle snap when done, which is the perfect contrast to the creamy sauce. Excess water can make the bake watery, so drying thoroughly is essential for a cohesive texture. One frequent error is over steaming; that yields floppy florets that fall apart during mixing. If your florets are uneven, cut larger pieces down a bit to ensure consistent cooking.
In a large saucepan melt 2 tablespoons of butter over medium-low heat; add the garlic and cook for 1 minute. Add the flour and stir for 1 minute.: The aroma of garlic blooming in warm butter fills the kitchen and signals that flavor is building. Cooking the flour briefly removes rawness and gives a nutty undertone to the roux. Stir constantly to form a smooth paste, and avoid browning the roux which could make the sauce grainy. People often rush this and end up with lumps, so use a whisk and moderate heat to keep things silky.
Add the cream cheese, blue cheese and milk or cream; stir over low heat until melted and smooth then stir in the broccoli florets.: As the cheeses melt, they form a glossy sauce that clings to the back of a spoon, and the scent becomes rich and tangy. Gentle heat prevents separation, and constant stirring helps incorporate the cream cheese fully. If the sauce looks broken or oily, reduce heat and whisk vigorously, adding a splash more milk to bring it back together. A common misstep is using high heat, which can cause the dairy to curdle and ruin the texture.
In a bowl combine the cracker crumbs with 6 tablespoons melted butter until well combined. Remove 1/2 of the cracker mixture and stir it into the broccoli mixture. Season with black pepper.: The scent of warm butter with crumbs is toasty and inviting, and folding half into the filling adds body and a subtle crunch throughout. Seasoning with black pepper at this stage helps distribute the spice evenly. Avoid adding too much pepper if your blue cheese is assertive. If the mixture seems too loose, stirring in the crumb portion helps bind liquid and improves stability during baking.
Transfer mixture into a casserole dish. Cover with foil and bake for 15 minutes.: Baking covered lets the interior heat through evenly and encourages the sauce to blend with the florets, while preventing premature browning of the topping. Steam trapped under the foil also keeps the dish from drying out. A typical mistake is leaving it covered too long, which can keep the topping from crisping later. Use a timer and peek gently at the edges to verify bubbling without lifting the foil unnecessarily.
Remove from oven and sprinkle the top with the remaining cracker crumbs. Return to oven and bake uncovered for another 10 minutes.: When you remove the foil, you should see gentle bubbling and hear a faint simmer, signaling proper doneness. Adding the remaining crumbs at this point ensures a golden, crunchy layer rather than a soggy top. Watch for a deep golden color rather than dark brown, because burnt crumbs will introduce bitterness. If the topping is not browning evenly, rotate the dish midway through this uncovered bake.
Allow to cool for 10 minutes before serving. Makes 4-5 servings.: Cooling lets the sauce set slightly so the portions hold their shape, and the aromas mellow into a balanced profile. Ten minutes also makes it safer to scoop without losing the crumb topping. A common error is serving immediately, which can lead to a runny casserole that spills; patience yields a cleaner, more attractive presentation. If you need firmer slices, let it rest a bit longer, but avoid leaving it too long or the topping can soften from steam.