Butternut Squash and Caramelized Onion Galette

Woke up craving caramelized onions, and finding more than half of one of my giant butternut squash in the fridge made me think the two together with dijon mustard and some drizzled truffle oil would be really tasty. Perfect for a fall day!
A Galette is nothing more than a free form rustic tart. You can also do this in a tart shell.
And i love truffle oil and use a lot in my cooking but you can omit that and just use olive oil if you prefer, and the smoked salt in the pastry can be swapped with regular salt or sea salt.

Ingredients:
Pastry:
1 stick cold unsalted butter, cut into 1 tablespoon slices
1 1/4 cup unbleached all purpose flour
1/2 teaspoon ground smoked salt
1 tablespoon fresh sage leaves, finely chopped
5 tablespoons ice cold water

Filling:
4 cups butternut squash, peeled and cut into cubes +1 tablespoon olive oil +1 tablespoon truffle oil + salt and pepper to taste
2 medium onions, thinly sliced into half moons + 2 tablespoons olive oil + 2 tablespoons butter + 1 tablespoon sugar + salt and pepper to taste
2 tablespoons dijon mustard
2 sage leaves, chopped
Truffle oil to drizzle

1 egg , well beaten

In a food processor pulse butter, flour, salt and sage leaves. Add water, 1 tablespoon at a time until dough crumbles. Pour over your work surface and form a ball with it. Wrap in plastic film and refrigerate for 1 hour.

Preheat oven to 375F.
Toss butternut squash, olive oil, truffle oil, salt and pepper and place it on a cookie sheet. Bake it on preheated oven for about 30 minutes.
While cooking the squash, go ahead and caramelize the onions by tossing all ingredients( onion, oil, butter, sugar, salt and pepper) together in a large frying pan and cook on low for about 45 minutes.
Toss butternut squash, onions and fresh sage in a bowl and set aside.

Turn oven temperature up to 400F.
On a floured surface roll out the dough to 14in round, doesn't have to be perfect, since it's a rustic tart.

Place on a ungreased cookie sheet. Brush mustard over the bottom of the pastry leaving about 2 inches around the sides of the tart. Top with squash and onion mixture. Drizzle with truffle oil(optional). Fold sides in, towards the middle, leaving the middle open. Brush beaten egg all over the top of crust.
Bake in preheated oven for 35-40 minutes. Let it rest about 10 minutes and then slice into wedges and serve as an appetizer. Serve warm, hot or even room temperature.