½cupoat flour -- you can make this by buzzing oats in a coffee grinder(45 grams)
1 ¼cupsall-purpose flour or pastry flour(150 grams)
1 ½sticksunsalted butter(170 grams)
¾teaspoonsalt
½cupice water
Peach Filling
1 ½poundsfresh peaches or nectarines
1tablespoonfresh lemon juice
¼cupgranulated sugar(50 grams)
½teaspooncinnamon
⅛teaspoonnutmeg
Oat Streusel
6tablespoonsunsalted butter, softened(84 grams)
½cuplight or dark brown sugar, packed(100 grams)
¼teaspoonsalt
1teaspooncinnamon
⅛teaspoonground nutmeg
½cupwhole wheat pastry flour or white whole wheat flour(50 grams) -- weigh for best results
1cupoats, rolled or "old fashioned" type
cream and coarse sugar for garnishingoptional
Instructions
Combine the oat flour and flour in a stand mixer bowl. Add the small chunks of butter. Using the paddle attachment of the stand mixer, mix on low speed until the mixture forms large clumps. Mix together salt and water and add to the crumbly mixture, stirring on low speed until it comes together in a shaggy mass.
Put some flour on a pastry mat and transfer the dough to the floured surface. Shape into a 5x8 inch rectangle. Dust with flour, then wrap in plastic and chill for at least an hour (preferably longer). When ready to use, place on a floured mat and let sit so that it's still cool but not so cold that it's difficult to roll.
On a floured pastry mat, roll into a rectangle around 6x12 -- doesn't have to be exact.
Fold the bottom third up to the center and the top third down over it. Dust with flour. Turn so that the short sides is facing you, then repeat the folding procedure three more times, rolling into a large rectangle, folding and turning By the time you finish most of the butter should be absorbed, while some of it should still be cold and show up as flecks. Wrap and chill for at least an hour until ready to use.
Make the streusel while the dough is chilling.
Prepare the streusel by stirring together the butter, sugar, cinnamon, salt and nutmeg in a medium bowl until combined. Stir in the flour until mixture is evenly moistened, then stir in the oats to make a crumbly mixture. Refrigerate until it's time to assemble the galette.
Let dough sit at room temperature for about 20 minutes or until it's not so cold you can't roll it easily. It should still be kind of cool. On a floured pastry mat, roll the dough into a 13 inch circle. Transfer to a 13x18 inch rimmed baking sheet lined with parchment paper. The dough will go over the edges a bit, but it will get folded inward. Note: If you are making the small version, use half the dough and roll into a 10 inch circle. Carefully transfer your dough circle to a big piece of parchment, then put the parchment and dough in the refrigerator to keep it cold while you slice the peaches.
Preheat oven to 400 degrees F.
Slice the peaches and toss with the lemon juice. If you are worried about mashing up your neat slices, squeeze the lemon juice onto a dinner plate and lay the slices in the lemon juice. Combine the sugar, cinnamon and nutmeg in a small bowl or cup and set aside.
Assemble the galette. Crumble the streusel over the dough circle, sprinkling it to an even thickness and leaving a 2 inch border of bare dough. As mentioned, you'll have a lot leftover. Starting at the outer edge of the streusel, arrange the fruit slices in concentric circles. Sprinkle the sugar mixture over the peaches, then fold the edges of the dough up and over the filling, pressing neatly to contain the peaches. Brush the sides of the galette with cream (or whole milk) and garnish with coarse sugar.
Bake for 35 to 40 minutes (it might take up to 45 if peaches are very juicy) until pastry is golden brown, juices are bubbling and the sugar on the fruit has caramelized. Remove from oven and let cool on a rack for 20 minutes before serving.
Notes
To make smaller Peach Galette, use half of the dough and save the rest. Use half the amount of streusel and about half the amount of peaches. Bake time stays the same.