Summer Strata with Spinach, Basil & Garlic Custard

This yummy summer dinner dish comes from a fun new blog that my roommate Sally introduced me to: eat me, delicious. There are also some killer baked goods dishes on her site. When Sally and I made this we halved the recipe - which was enough for about five servings. The one below should serve ten.

Caramelized Onions (start this early!)
1 tbsp butter
1 tbsp olive oil
4 yellow onions, sliced
1 tsp salt
1/2 tbsp brown sugar
1/2 cup white wine
1/4 cup vegetable stock or water
2 tsp balsamic vinegar
1/4 tsp freshly-ground pepper
1 tsp minced fresh thyme, sage or rosemary (or a combo)

Filling
1 lb sourdough loaf, cut into 3/4" cubes (you could use whatever bread you wanted - we used a simple white-whole wheat loaf)
2 bunches of spinach, wilted, squeezed and chopped OR a big bag of baby spinach (no need to prep, it'll wilt when it's being baked)
1 recipe caramelized onions
1/2 cup sundried tomatoes (not oil packed)
1/2 cup chopped basil
1/2 cup chopped parsley (optional)
1 1/2 cups grated fontina cheese, divided

Custard
6 eggs
2 1/2 cups milk (no-fat is fine)
2 bulbs roasted garlic, mashed OR four cloves raw garlic, minced
1 1/2 tsp salt
1/2 tsp freshly-ground pepper

Caramelized Onions
1. Heat olive oil and butter over medium heat until the butter begins to foam. Add the onions and stir to coat. Add salt and cook for 20 minutes. Stir occasionally.

2. Sprinkle in the sugar and wine and reduce until the liquid has evaporated. Add stock, vinegar, pepper and herbs. Cook gently until the stock is reduced and the onions reach a creamy texture.

Filling and Custard
1. Soak the sundried tomatoes until soft, strain and chop coarsely.

2. To make the custard, whisk the eggs in a large bowl. Whisk in the milk, cream, mashed roasted garlic, salt and pepper. Stir in the bread cubes, cover and let stand for up to 1 hour. Stir occasionally to ensure that all of the bread is evenly soaked. Stir in the remaining filling ingredients, reserving half of the grated cheese.

3. Heat the oven to 350F. Butter or oil a 9"x13" baking dish and scoop the bread pudding mixture into it. Sprinkle with the reserved cheese and bake until crusty, golden brown and just set in the middle (about 45 minutes). Let stand for several minutes, cut into squares and serve.