caramelized onion and mushroom casserole with broccoli

Whenever I make a pasta casserole, I always think this one will be different. That this one will be the new and exciting one that's the casserole to stake my life on. Which is almost never true. That would be my mac and cheese, or the broccoli and cauliflower gratin that dinner guests request from me years later. This casserole is right in the middle. It's not something that I'd set out for Sunday dinner or as the main course when I'm having friends over ... but as a side dish or a weekday meal? This is pretty darn lovely.

My basic pasta casserole, filled with whatever's easy and in the fridge, never end up being life changing. It's pretty formulaic: pasta, vegetable, bechemel based sauce, sometimes meat if I have some on hand. Variations of this can be done simply, with frozen vegetables. It can be done somewhat easily, with just some broccoli thrown in. It's all very basic. This one, though, it has a little something special going for it.

There's a bit of a time commitment here, caramelizing the onions and sauteing the mushrooms. It's worth every second though as that's what makes this casserole just oh so good. It adds more body and depth ... so much that you could (if you were so inclined) skip the broccoli altogether and just double (or triple) mushrooms and onions. It would probably be pretty decadent.

I was also a bit crazy and tried to do everything all at once. Give yourself a break and make things in stages. It will really, really help your sanity. Then? Enjoy how deliciously lovely this is.

Oh? This will comfortably serve four for dinner as a main ... but you'll probably wish there were some leftovers.

Caramelized Onion and Mushroom Casserole with Broccoli

Ingredients:

For the casserole filling

• 4 cups dry, medium pasta
• 2 cups broccoli florets
• 3 medium white or yellow onions, chopped
• 3 cups cremini mushrooms, halved
• 1 tablespoon olive oil
• 1 tablespoon butter
• 1 teaspoon salt
• 1/2 cup grated parmesan

For the sauce:

• 3 tablespoons butter
• 3 tablespoons flour
• 3 cups milk
• 1 tsp salt
• 1 tsp white pepper
• 1/2 tsp oregano
• 1/2 cup shredded old cheddar (optional)

Directions

1. Preheat your oven to 350*F.
2. Make the caramelized onions and mushroom mixture.
1. In a medium sized skillet over on medium high heat, heat the olive oil until sizzling. Add the onions to the skillet. Lightly salt to taste (about 1/2 tsp if you're me.) 
2. Cook until caramelized, stirring frequently. This is going to take about fifteen to twenty minutes as the onions first go translucent, then brown, then start to get really fragrant and brown. Bits of onion will be starting to stick to the pan at the end. Add butter to the onions and allow to melt.
3. Add mushrooms to the pan, and stir. Cook the mushrooms together with the onions another five minutes, or until the mushrooms have shrunk by about half. Cooking the mushrooms in the onions allows the onions to continue to deepen their flavour without cooking too intensely, and lets the mushrooms pick up some of the caramel-y goodness.
4. Remove from the heat and set aside for later
3. Make your sauce.
1. In a medium saucepan again over medium heat, melt butter. Add the flour, wisk together until evenly incorporated with no lumps. Cook it about 3 minutes, letting the roux bubble a bit and stirring so it doesn't burn. This cooks off the flour so your sauce won't taste floury.
2. Add the milk. Wisk vigourously to get the roux incorporated. Continue to cook, wisking occasionally, until thickened. To thicken entirely, the mixture needs to come to a light, bubbly simmer at the least. Because there's such a high milk to roux ratio (to keep the casserole nice and moist) you want this to thicken as much as it will.
3. Wisk in the salt, pepper and oregano.
4. Turn the heat down to the minimum and add in the cheddar. Wisk until completely melted into the sauce, remove from heat and set the sauce aside.
4. Make your pasta.
1. Bring a large pot of salted water to a boil and cook the pasta according to package directions.
2. In the last two to three minutes of cooking throw the broccoli into the pot. This allows the broccoli to begin the cooking process so it will come out of the casserole properly cooked.
3. Drain.
5. Assemble your casserole.
1. Pour your pasta and broccoli into the casserole dish. Pour the onions and mushrooms on top, scraping the pan to make sure you get all the yummy caramelized bits.
2. Pour your sauce overtop of the casserole components.
3. Give it all a good mix, making sure there's a little bit of broccoli and a good distribution of onion and mushrooms in every bit of the pan. You can eyeball this - it's pretty obvious when you've got a good mixture of things.
4. Sprinkle the parmesan cheese overtop for just a little bit crunch.
6. Bake for 20-25 minutes. Eat. Have some seconds, because you probably will.