At least an hour before cooking, pour the beer into a shallow bowl to sit until it becomes flat. Dry the bread cubes on a baking sheet in a 300F oven until they are crisp but not browned, probably about 15 to 20 minutes. Saute the cauliflower in the butter with the caraway seeds until just barely tender.
Combine the bread cubes and cauliflower with the grated cheese. Spread the mixture into a buttered 2-quart casserole dish. Mix the eggs, mustard, coriander, and black pepper in a blender or by hand with the flat beer and pour the mixture into a casserole dish. Bake at 350F for 30 to 45 minutes until puffed and golden.