1/2cup(50 grams) ground hazelnuts or hazelnuts, toasted
1/4cup(50 grams) sugar
1tablespoon(10 grams) all-purpose flour
4tablespoons(56 grams) unsalted butterroom temperature
1(50 grams) large eggroom temperature
3large applespeeled and quartered
3tablespoons(37 grams) dark brown sugar
1(50 grams) large egg
2teaspoonsmilk or heavy cream
Make the Pie Dough
Put the flour, sugar and salt in a bowl and stir to combine. Place the flour mixture into a food processor.
Cut the butter into 1/2-inch cubes and add it to the flour mixture. Pulse the dough until it is coarse and crumbly, and the butter is about the size of peas.
Pour the mixture into a large bowl. Add 1/4 cup of ice water and use a rubber spatula to toss together. Add the remaining water and mix into the dough until it starts to come together. It will still be slightly crumbly or shaggy but will hold together when squeezed into a ball. If more water is needed add a tablespoon at a time.
Dump the dough onto a lightly floured surface and press the dough together, folding it over on itself until it starts to hold together. Try not to work the dough too much or it may become and overdeveloped and tough.
Divide the dough into 2 equal parts and shape each piece into disk 1-inch thick. Wrap each disk in plastic wrap and chill for at least 45 minutes. I use one disk for this recipe and freeze the other for another dish. The dough can be refrigerated for up to 3 days and frozen for up to 2 months.
Make the Hazelnut Frangipane
Hazelnut Flour: Put the hazelnut flour, sugar, all-purpose flour, salt and cinnamon a bowl and whisk until the mixture is well combined.
Whole Hazelnuts: In a food processor, fitted with a metal blade, place the hazelnuts, sugar, flour, cinnamon and salt and process until the hazelnuts are very fine. Empty the mixture into a bowl and set aside.
In a medium sized bowl with a handheld mixer beat the butter until creamy. Beat in 1/2 the hazelnut mixture until incorporated, then beat in the egg. Add the remaining hazelnut mixture and beat until incorporated. Beat in the vanilla. Refrigerate for at least 10 minutes.
Assemble the Galette
Preheat the oven to 400 degrees F.
In a small bowl combine the brown sugar, cinnamon and nutmeg and whisk together. Cut each apple quarter into 5 slices. Keep the slices together and place in a large bowl.
Remove the pie dough from the refrigerator and roll into 12-inch circle. Fold the dough in half and lift it into the cast iron skillet. Unfold it and gently press the dough in the bottom and the sides of the skillet. Spread the hazelnut frangipane across the bottom the dough.
Arrange the apples across the bottom of the dough. To get the look featured in the recipe keep the apple slices together and arrange the group in a pattern of your choice. Sprinkle the brown sugar mixture over the apples.
Fold the edges of the dough over the apples, creating overlapping folds as you work your way around the dough. Whisk the egg and the milk together. Brush the dough with the egg wash, including under the dough folds. Sprinkle generously with turbinado sugar.
Bake in the oven for 35-40 minutes until it is golden brown. Rotate the pan after the first 15 minutes to ensure even browning. Remove it from the oven and allow to cool for 10-15 minutes before serving.
The hazelnut frangipane can be stored in the refrigerator for 3 days.