Begin by frying the chopped bacon in a skillet over medium heat until it’s crispy and golden, about 8-10 minutes.

Transfer the bacon to a paper towel-lined plate to drain excess grease and cool. Reserve 2 tablespoons of the bacon fat in the skillet.

In the same skillet, add the chopped yellow onion and cook over medium heat for 5 minutes.

Stir in the minced garlic and fresh spinach, cooking for another 2-3 minutes until the spinach wilts.

In a large mixing bowl, whisk together 6 eggs, 2 cups of half and half, salt, black pepper, and chopped chives.

Grease a 9x13-inch baking dish and begin layering it with the day-old bread cubes.

Sprinkle half of the shredded Swiss and cheddar cheeses over the bread, then add the sautéed mixture of bacon, onions, and spinach.

Pour the egg custard mixture evenly over the layers and finish with the remaining cheese.

Cover with plastic wrap or foil and refrigerate for at least 6 hours, or overnight.

Remove from the refrigerator and let it sit at room temperature for 20 minutes.

Preheat your oven to 350°F (175°C) and bake uncovered for 35-40 minutes.