How to Make It
Preheat oven to 475°F. Toss together bread, 2 tablespoons oil, 1/2 teaspoon salt, and 1/4 teaspoon pepper on a rimmed baking sheet. Bake in preheated oven until bread is golden brown and crisp, 4 to 6 minutes, stirring once after 3 minutes. Remove from oven; set aside. Reduce oven temperature to 425°F.
Place a rimmed baking sheet in oven; let warm at 425°F 10 minutes. Toss together broccoli steaks, tomatoes, onion wedges, 2 teaspoons salt, 1 teaspoon pepper, and remaining 1/4 cup oil in a large bowl. Arrange mixture in a single layer on preheated pan. Bake at 425°F until broccoli is tender and charred in spots, 20 to 25 minutes, flipping broccoli and onion after 10 minutes. Remove from oven.
Transfer tomatoes, onion, and 1/4 cup stock to a blender. Secure lid on blender, and remove center piece to allow steam to escape. Place a clean towel over opening. Process until smooth, about 30 seconds, adding remaining 1/4 cup stock, 1 tablespoon at a time, as needed to thin sauce to a pourable consistency. With blender running, gradually add butter, processing until sauce is glossy and thick, about 20 seconds. Stir in remaining 1 teaspoon salt and remaining 1/2 teaspoon pepper.
Spoon about 1/4 cup tomato sauce onto each of 4 plates. Top with broccoli steaks, tapenade, and toasted breadcrumbs.