Heat the oil in a 10-inch skillet over medium heat. Meanwhile, peel and coarsely chop the onions, adding them to the skillet as you chop. Cook, stirring occasionally over medium heat until soft and caramelized, about 7 minutes.
While the onions are cooking, place the spinach on a microwave-safe plate and cook on high power for 3 minutes, or until thawed well. Some ice crystals may remain, which is fine. Place the defrosted spinach in a colander and press to remove as much water as possible. Leave to drain.
In a large bowl, crack the eggs and add the milk and 1 cup of the cheese. Add the drained spinach. Whisk to mix well.
Spray a 13-by-9-inch glass casserole dish with cooking-oil spray. Cut the bread into 1-inch cubes and place them in the dish. When the onions are caramelized, toss them with the bread cubes, making sure to combine well. Slowly pour the egg mixture over the bread cubes and onions. Press the bread cubes down into the egg mixture, making sure they are completely soaked. Sprinkle the remaining cheese over the casserole, add salt and pepper, and cover tightly with plastic wrap. Refrigerate for at least 4 hours or overnight.
Preheat the oven to 350 degrees. Bake the casserole for 1 hour or until hot and bubbling along the edges. Remove from the oven and let rest for 5 minutes. Cut into squares and serve.

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Nutrition Facts

Per Serving Per 100 g

Amount Per 1 Serving
Calories	329.51 Kcal (1380 kJ)
Calories from fat	134.62 Kcal
		% Daily Value*
Total Fat	14.96g	23%
Cholesterol	162.22mg	54%
Sodium	514.19mg	21%
Potassium	374.42mg	8%
Total Carbs	28.57g	10%
Sugars	6.5g	26%
Dietary Fiber	2.15g	9%
Protein	21.05g	42%
Vitamin C	3.8mg	6%
Vitamin A	0.3mg	9%
Iron	2.6mg	15%
Calcium	424.5mg	42%

Amount Per 100 g
Calories	139.99 Kcal (586 kJ)
Calories from fat	57.19 Kcal
		% Daily Value*
Total Fat	6.35g	23%
Cholesterol	68.92mg	54%
Sodium	218.45mg	21%
Potassium	159.07mg	8%
Total Carbs	12.14g	10%
Sugars	2.76g	26%
Dietary Fiber	0.91g	9%
Protein	8.94g	42%
Vitamin C	1.6mg	6%
Vitamin A	0.1mg	9%
Iron	1.1mg	15%
Calcium	180.3mg	42%

* Percent Daily Values are based on a 2000 calorie diet. Your daily values may be higher or lower depending on your calorie needs.
Find out how many calories should you eat.

Tastes

salty
savory
bitter
sweet

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