Apricot, Sage and Hazelnut Galette

1 1/2 cups all-purpose flour
1 1/2 tablespoons white granulated sugar
1/2 teaspoon fine-grain sea salt
1 stick unsalted butter, frozen
1 large egg
1/4 cups buttermilk, shaken, plus 1 tablespoon-2 tablespoons, divided

1/4 cup hazelnuts (about 15-16 hazelnuts)
4-5 apricots, sliced
6 tablespoons white granulated sugar
1 1/2 tablespoons minced fresh sage (5-6 leaves)
1 tablespoon corn starch
Pinch salt

1 large egg, beaten with a splash of buttermilk 
Turbinado sugar

1. In a large bowl, combine the dry ingredients: flour, sugar and salt. Using a box grater, grate the cold butter atop the flour mixture. Working quickly, and using your hands, break the butter bits into the flour until they're evenly distributed and resemble the size of small peas. Beat together the egg and 1/4 cup buttermilk and add it to the flour mixture. Mix the dough together until it just begins to climb together; if the dough doesn't hold together, add an extra tablespoon or two of buttermilk. 

2. Remove the dough from the bowl and place it on a lightly floured counter. Knead the dough a few times until it comes together and shape it into a mound. Shape the dough into a disc and wrap it plastic wrap; transfer it to the refrigerator to chill for 1 hour or overnight. 

3. While the dough is chilling, turn your attention to the filling. Preheat the oven to 350 degrees F. Spread the hazelnuts onto a baking sheet and roast in the oven for 15 minutes, until they turn a dark brown color. Carefully transfer the hot hazelnuts to the center of a clean kitchen towel. Wrap the towel around the hazelnuts and rub them back and forth, which will shake off their skins. (If some of the hazelnuts have a bit of a skin still attached, no biggie!). Chop the hazelnuts, roughly; transfer them to a medium bowl. Add the sliced apricots, sugar, fresh sage, cornstarch and pinch of salt. Toss together and set aside. 

4. Remove the disc from the refrigerator. Heavily flour your work surface and rolling pin. Roll out the dough, being sure to rotate it every so often so it doesn't stick, until it reaches a 1/8-inch thickness. Cut the dough into one large 13-inch circle (I used a 13-inch plate as a guide). Transfer the dough circle to the center of a parchment-lined baking sheet. Reroll the scraps and slice ten-twelve strips that are about 12-inches long and about 1 1/2-inches wide. 

5. Spoon the filling out of the bowl (leaving any fruit juice behind) and place it in the center of the dough circle, leaving a 1/2-inch border around the sides. Arrange the fruit so it's in one layer (not topped onto each other). Make it look pretty, if you like! Fold over the sides. 

6. Lay the strips onto the top, making a lattice top (step-by-step instructions here). Trim the edges with a sharp knife. Make sure to secure the edges of the dough with a little water, pressing the lattice strips and the folded over sides together just enough to bind the two. This way nothing's going anywhere when it gets in that hot oven. 

7. Place the baking sheet in the freezer for 15 minutes. Meanwhile, preheat your oven to 400 degrees F. Right before entering the oven, brush the top of the galette with egg wash and sprinkle on a bit of turbinado sugar. Bake for 20-25 minutes, until medium golden brown. Transfer to a cooling rack until the galette is room temperature. 

Makes one 12-inch galette