Trim the stems from the broccoli florets. You want bite-sized pieces or a little larger. Chop the shallot and mince the garlic.
In a medium to large pot, melt the butter over medium heat. Cook the shallot and garlic in the butter for a minute or two. Whisk in the flour, as this will create a paste consistency.
Then whisk in the milk and stock, which will create a very thin roux or gravy-like consistency.
Then stir in the cheese and continue to cook and stir until the cheese is melted.
Season this mixture with a little salt and pepper and then stir in the broccoli so it all gets coated.
Pour this mixture into a square (8×8) baking pan. Cover with aluminum foil and bake at 350°F (177°C) for 30 minutes.
Meanwhile, prepare the cracker topping. In a food processor, grind the crackers into crumbs (you can also do this in a ziplock bag with a rolling pin).
Then stir in the melted butter and seasoning.
Once the casserole has baked for the initial 30 minutes, remove it from the oven. Take off the foil and sprinkle the cracker topping all over.
Bake for an additional 6-8 minutes. The cracker topping should deepen in color and the casserole should be bubbling along the sides.
Notes
If you like, you could top this casserole with something crunchy beyond Ritz crackers, like French fried onions.Allow to cool slightly before serving. If you serve the casserole piping hot right from the oven, it will be more liquid-y.