Cheese & Onion Casserole

Think of this as a savory bread pudding with serious cheese flavor. Layers of buttered day-old bread alternate with a sauteed onion and melted cheddar mixture spiked with dry mustard, then the whole thing gets soaked in milk and baked for an hour until puffed and golden.

Sauteing the onions until golden before mixing them with the cheese is what gives the sauce its depth. Raw onions would taste sharp and harsh. Cooked onions bring a mellow sweetness that plays perfectly against the sharp cheddar and the bite of the mustard.

Day-old bread is ideal here. Fresh bread turns to mush too quickly. Stale bread absorbs the milk slowly, keeping its structure long enough to bake into distinct layers with pockets of melted cheese between them.

Pro Tips

• Use sharp cheddar for the most flavor. Mild cheddar melts nicely but tastes flat in a dish this simple.
• Don’t skip the dry mustard. It’s a tiny amount but it sharpens the cheese flavor dramatically. Without it, the casserole tastes one-dimensional.
• Pour the milk evenly over the top and let it sit for 5 minutes before baking so it has time to soak into the bread layers.
• The casserole is done when the top is puffed, golden brown, and the center doesn’t jiggle when you shake the dish.

Variations

• Bacon cheddar: Lay crumbled cooked bacon between the bread layers for a smokier, meatier version.
• Gruyere version: Swap the cheddar for Gruyere and add a pinch of nutmeg for a French onion soup-inspired casserole.
• Broccoli cheddar: Tuck steamed broccoli florets between the layers for added vegetables and color.