Galettes are the best reason for being messy, careless, and still end up with a beautiful dessert that will evoke many "oohs and ahhs" from your loved ones. This galette is extremely flaky and moist thanks to the 1:1 ratio of butter and olive oil in the crust dough. Pair up cinnamon-y apples with a rich mascarpone custard filling and you've got yourself the coolest dessert for that professional chef in your family (speaking from experience). The crust dough can always be made ahead of time, which will cut down your work load and time in the kitchen during the busy holiday months. Enjoy! —Ellie Betzen
Let's begin with the crust. Mix flour, salt, and sugar in a large mixing bowl. Grate butter through the medium holes in the box grater into the dry ingredients, add oil, egg white, and water. Knead and incorporate with your hands so it becomes mushy and crumbly. Be aware that due to the addition of oil, you will end up with a moist and gritty dough. Form into a ball, seal with plastic wrap, and freeze for about 20 minutes. Or refrigerate if you are making it a day ahead of time.
Now onto the filling. Preheat the oven to 375 F (191 degrees celsius). Start a sauce pan on the stove at low-medium heat. Cook egg yolks while stirring constantly for about 30 seconds, whisk in mascarpone cheese, sugar, and vanilla gradually in that order. Keep whisking to prevent burning and if it bubbles, lower the heat a little more. Cook for about 4 minutes. Set aside. Coat the peeled apple slices with cinnamon in a large bowl and set aside.
After 20 minutes are over, roll the dough onto a floured surface and make it into a circle or oval of about 1/4 inch in thickness. It should be quite large and nicely spread out. Now is the time to transfer the dough onto a large baking sheet to prevent it from ripping later.
Place apple slices in the middle of the dough and spread them out as much as possible, but leave about 3-4 inches of space in the edges of the dough so you can seal them up. Very carefully pull up a section of the edge towards the middle so it covers some of the apple slices. You might have to slide a large, sharp knife under the dough to peel it off the flat surface, if need be. Repeat this process all around the edge. Pour the mascarpone custard over the fruit so it trickles through and some of it falls to the bottom. Brush the top of the dough with egg wash and bake for approximately 25-30 minutes, or until it's slightly golden on top. Open the oven, brush with egg wash one more time and sprinkle with sugar (optional). Bake for another 3 minutes. Let it cool and serve with ice cream if you like!