Ingredients
2 lb. crusty country bread (about 2 loaves), preferably sourdough, cut into 1 1/2″ pieces
6 Tbsp. unsalted butter, divided, plus more for dish
1 large yellow onion, chopped
2 medium leeks, tough outer layer removed, thinly sliced into half-moons
4 cloves garlic, finely chopped
Kosher salt
Freshly ground black pepper
2 large eggs
2 1/2 cups low-sodium chicken broth
1 1/2 cups whole milk
2 Tbsp. mixed chopped fresh herbs, such as sage, rosemary, and/or thyme
Pinch of crushed red pepper flakes

Directions
Step 1
Preheat oven to 350°. Spread bread between 2 baking sheets. Bake bread, tossing halfway through, until crispy and feels dry and the edges are just starting to turn golden, 15 to 20 minutes.
Step 2
Meanwhile, in a medium skillet over medium heat, melt 3 Tbsp. butter. Cook onion and leeks, stirring occasionally, until softened, about 7 minutes. Add garlic and cook, stirring, until fragrant, about 1 minute more; season with salt and black pepper. Let cool slightly.
Step 3
In a medium bowl or large glass measuring cup, whisk eggs, broth, milk, herbs, and red pepper; generously season with salt and black pepper.
Step 4
Increase oven temperature to 375°. Grease a 13″ x 9″ baking dish with a thin layer of butter.
Step 5
Transfer bread to a very large bowl. Add onion mixture and egg mixture and toss to combine. Let sit at least 10 minutes or up to 1 hour.
Step 6
Transfer bread mixture to prepared dish and spread in an even layer, making sure all liquid makes it into dish. Cut remaining 3 Tbsp. butter into small pieces and dot over top. Cover with foil.
Step 7
Bake stuffing 20 minutes. Uncover and continue to bake until top is golden brown and crisp, 25 to 30 minutes more. Serve warm or at room temperature.