Roasted Broccoli Steaks with Tomato Butter and Tapenade

Ingredients

2 ounces bakery white or rye bread, torn into small pieces (about 1 cup)
6 tablespoons olive oil, divided
3 1/2 teaspoons kosher salt, divided
1 3/4 teaspoons black pepper, divided
2 medium broccoli heads, stems trimmed to 3 inches and heads cut lengthwise into 8 (3/4-inch-thick) steaks
2 cups cherry tomatoes (about 10 ounce)
1 small red onion, cut into 1-inch wedges (root trimmed)
4 to 8 tablespoons unsalted vegetable stock
2 tablespoons unsalted butter, chilled and cut into 1/2-inch pieces
1/4 cup jarred tapenade (such as Divina Olive Bruschetta)