Pulse bread in a food processor to form medium-fine crumbs.
Spread in a 4-sided sheet pan and toast in oven, stirring occasionally, until golden, 8 to 10 minutes. Cool.
Core cauliflower, keeping head intact, then cook in a large steamer rack over boiling water, covered, until tender, about 15 minutes.
Transfer to a platter and keep warm, covered.
Melt butter in a large heavy skillet over medium heat and stir in caraway seeds, toasted crumbs, 1/2 teaspoon salt, and 1/4 teaspoon pepper. Cook, stirring, until hot, about 2 minutes. Spoon over cauliflower.
Crumbs can be toasted 1 day ahead and kept in a sealable plastic bag at room temperature.
