I am an unapologetic butternut squash enthusiast, and this butternut squash galette is one of my favorite ways to use this sweet, nutritious squash. It's sweet and delicate, and a gorgeous centerpiece for a gathering with friends.
Cut the butter into 1/2" cubes and then re-chill for about 5 minutes. Pour 1/2 cup of water into a small dish and along with a handful of ice cubes.
Add the butter to the flour along with 1 tsp sea salt, and then use your fingers or a pastry cutter to break up the butter until it is coarsely incorporated. You want largish chunks of butter to remain, as these will melt and create tiny little pockets of amazingness once the dough cooks.
Working with a tablespoon at a time, add water to the flour/butter mixture until it just comes together. Do not overwork the dough. You want enough water so that the dough barely stays together when formed into a ball.
Wrap the ball of dough in plastic wrap and chill at least 1 hour, or up to overnight.
When you're ready to make the galette, remove the dough from the freezer, dust some flour on your work surface, and roll out the dough in a circle to a scant 1/2" thickness. The dough will be about 12" in diameter. Transfer the dough to a parchment lined baking sheet.
While the dough is chilling (or just before you remove it from the fridge), prepare the filling. Preheat the oven to 400 and the prepare two baking sheets with parchment paper.
Peel and seed the butternut squash. Cut lengthwise, and then slice to about 1/2" thick. Toss with 1 tablespoon of olive oil and spread over one baking sheet. Roast for about 30 minutes, flipping pieces halfway through.
While the squash is cooking, prepare the caramelized onions. Heat a skillet over medium heat and add the remaining tablespoon of olive oil. Reduce heat to medium-low, and cook the onions until browned and soft, 20-25 minutes. In the last couple of minutes, add the balsamic vinegar and allow it reduce and thicken.
Once the vegetables are cooked, prepare the galette. Place the caramelized onions on the center of your galette, spreading to a circumference of about 8". Top them with some fresh thyme, salt and pepper. Sprinkle the cheese over the onions. Then, top the cheese with the squash slices and more fresh thyme, salt, and pepper. Fold up the edges of the dough towards the center, gently pleating as you make your way around the galette.
Beat the egg with 1 tablespoon of water, and brush the crust with the egg wash.
Bake at 400 for 30-40 minutes until the crust is golden brown. Let stand for 5-10 minutes and then slice and serve.