Caramelized Onion Cauliflower Tart: My favorite side

I don't know about you but side dishes are my favorite part of Thanksgiving. My plate generally is separated into piles of green bean casserole, stuffing, sweet potatoes and above all else my mom's mashed potatoes (although my MIL makes a mean one too) and two measly pieces of turkey.  Since Thanksgiving is just around the corner, I wanted to share one of my favorite fall recipes that would make a fantastic, unique side dish for your Thanksgiving meal. I offered to bring this tart to my in-laws last year but got lazy and didn't make it...I am one amazing daughter-in-law/house guest aren't I?  Anyway, here is the original recipe, with my lazier adaptation below.  You won't be disappointed, the smell alone is worth it!

Cast of Characters:
- 1 small head of cauliflower, chopped into small florets
- 3 and 1/2 tbsp of olive oil
- Salt and pepper
- Truffle oil or truffle salt*
- 1 medium onion, sliced
- 2 large eggs
- 1/2 cup of heavy whipping cream**
- 1 8oz container of mascarpone cheese***
- 1 cup of grated Gruyere cheese (Swiss is a good substitute, I used cheddar as I had it on hand but a milder cheese is your best option)
- 1/4 tsp of black pepper
- A sprinkle of nutmeg
- 1 tbsp of Dijon mustard
- 1 frozen deep dish pie crust
- Grated Parmesan cheese for sprinkling

1) Pre-heat your oven to 425 degrees. Chop your cauliflower and add to a bowl containing 2.5 tbsp of olive oil. Coat cauliflower with oil, add salt and pepper and pour onto a baking sheet.  Place in the oven for 15 minutes, stir and roast for an additional 15 minutes (10 in my oven) until brown and tender. *Drizzle with truffle oil or truffle salt and let cool. You can absolutely skip this step; I have every time until this one because truffle anything is PRICEY but my co-worker Ro gifted me some truffle oil a few weeks ago. Thanks Ro!

2) Reduce oven temperature to 350 degrees. Add remaining 1.5 tbsp of olive oil to a large skillet, add sliced onion, salt and pepper. Cook onions down over medium-low heat for 30-40 minutes or until golden brown and soft.

3) Meanwhile spread 1 tbsp of Dijon mustard across the bottom and along the sides of the pie shell. I needed just over 1 tbsp to accomplish this.

4) In a bowl whisk together eggs, mascarpone cheese, heavy cream, 1/4 tsp of black pepper and grated nutmeg in a bowl.  Stir in grated Gruyere/Swiss/whatever cheese you use.

5) Place pie pan on a baking sheet to prevent spill over, and then layer onions on the bottom, cauliflower in the middle and thecheese/egg/cream mixture on top.  Sprinkle grated Parmesan on the top.  Bake for 40 minutes at 325, until firm and golden brown.

This tart is creamy and tangy. The combination of Dijon mustard, onions and roasted cauliflower is delicious.  It's great hot or cold, and also makes for a delicious brunch option with a side salad.  **You can use light cream or even milk if you are trying to be calorie conscious, but the tart is best with heavy cream.  *** Sour cream can be substituted for marscapone cheese in a pinch if you can't find it.  Also, if you are an overachiever, you can make your own dough, but in my humble opinion pre-made pie crust has come a long way and works just fine for this tart.  If you do make your own, make sure to make it big enough for a deep tart pan as the filling needs a lot of space.
 
What are some of your Thanksgiving favorites?  Sides, turkey and gravy, pumpkin pie?  Do you stick with tried and true family recipes, or try something new for an audience?