How to Make It
Preheat the oven to 450°. Heat a large rimmed baking sheet in the oven until it is very hot to the touch. In a large bowl, toss the broccoli spears with the bread cubes, olive oil and garlic and season generously with salt and pepper. Spread the broccoli and bread cubes on the hot baking sheet and roast for about 15 minutes, turning once, until the broccoli is tender and browned in spots and the bread cubes are crisp and golden.
Meanwhile, in a small saucepan, heat the cream until boiling. In a small bowl, whisk the egg yolk. Gradually whisk in the hot cream. Return the mixture to the saucepan and cook over low heat, whisking constantly, until it is slightly thickened, about 2 minutes. Off the heat, add the Fontina and stir until melted. Pour the fondue into a bowl. Transfer the broccoli and bread to plates and sprinkle with the marjoram and balsamic vinegar. Serve with the fondue.