Step 1

Butter a 3-quart baking dish with 1 tablespoon butter. In a large skillet, melt 2 tablespoons butter over medium-high. Add bacon, onion, and garlic and cook until onion is softened, about 2 minutes. Gradually add spinach to skillet and cook, stirring occasionally, until just wilted, about 2 minutes. Season with salt and pepper.

Step 2

In a medium bowl, whisk together eggs, milk, and nutmeg. Season with salt and pepper.

Step 3

Scatter half the bread in dish and top with half the spinach mixture and half the cheese. Top with remaining bread, spinach mixture, and cheese. Pour egg mixture into dish and gently press bread to submerge. Cover and refrigerate at least 2 hours (or up to overnight).

Step 4

Preheat oven to 400 degrees. Uncover dish and bake until bread is golden brown and custard is just set, 45 to 50 minutes (cover with foil if browning too quickly). Let cool 5 minutes before serving.