Oven-dry the bread:
Heat the oven to 300°F. Slice the bread 3/4 inch thick. Spread the bread slices directly on the oven rack and bake until crisp all the way through (most of the moisture in the bread will be evaporated) and lightly browned, about 15 minutes.
Cut the bread into 3/4-inch cubes (about 6 cups).
Roast the garlic:
Heat the oven to 350°F. Put the garlic in a small shallow baking dish, pour the vegetable oil over it, and cover with foil. Bake until the garlic is browned and soft, 50 to 60 minutes. Let cool. Pick or squeeze the pulp out of the garlic cloves and purée the pulp in a food processor; you should have about 1/3 cup. The purée can be made ahead of time and refrigerated until ready to use.
Cook the onions:
Heat the olive oil in a large nonstick skillet over high heat. When the oil is hot but not smoking, reduce the heat to medium and add the onions, salt, and pepper. Cook until the onions become soft and golden, 30 to 40 minutes. Add the vinegar and sugar; cook until the liquid is absorbed, about 3 min.; you should have about 1-1/2 cups. The onions can be made ahead of time and refrigerated until ready to use.
Make the pudding:
Heat the oven to 350°F. In a large bowl, whisk together the cream, eggs, egg yolks, roasted garlic, rosemary, salt, and pepper. Stir in the caramelized onions and the bread. Let sit for 30 minutes. to saturate the bread, stirring occasionally.
Brush a 2-qt. (or 9x13-inch) baking dish evenly with the butter. Pour the bread mixture into the baking dish, distributing the ingredients evenly. Bake in the hot oven until lightly browned and firm, 40 to 45 minutes.
nutrition information (per serving):
based on ten servings;
Photo: Rita Maas