How to Make It
Melt the butter in a medium pot over medium heat Add the flour and cook, whisking, until foamy, about 30 seconds. Whisk in the milk and bring to a boil. Reduce heat and simmer, stirring often, until thickened, 8 to 10 minutes.
Add the cauliflower. Cook, stirring occasionally, until tender, 8 to 12 minutes. Remove from heat and stir in the Gruyère, 1 teaspoon salt, and ¾ teaspoon pepper.
Top with the bread crumbs. Let rest for 10 minutes before serving. Serve warm.