Preparation

Make the dough

• Pulse the flour, sugar, rosemary, and salt in a food processor fitted with a metal blade. Add the butter, and pulse until the mixture looks like coarse meal. Sprinkle 1/4 cup of the water over the mixture, and pulse to combine. Gently squeeze a handful of crumbs; they should hold together. If they easily break apart, add water 1 Tbs. at a time, up to an additional 1/4 cup, pulsing and then checking the consistency after each addition. Dump the mixture onto a work surface, form into a ball, then flatten into a disk. Wrap in plastic wrap, and refrigerate for a minimum of 45 minutes or up to two days.

Make the filling

• Melt the butter in a large skillet over medium heat. Add the leeks, 1/2 tsp. of the fine sea salt, and 1/8 tsp. pepper, and cook, stirring occasionally, until the leeks are tender, adding more butter if the pan becomes too dry, about 8 minutes. Reduce the heat to low, add the cream, and cook, stirring frequently, until thickened, about 1 minute. Set the leeks aside to cool.
• In a large bowl, toss the potatoes with the oil, 1/2 tsp. fine sea salt, 1 tsp. of the rosemary, and 1/2 tsp. of the lemon zest. In a small bowl, lightly beat the egg with 1 tsp. water to make an egg wash; set aside.

Make the galette

Position a rack in the center of the oven and heat to 400°F.

Lightly flour the dough, a rolling pin, and a piece of parchment cut to fit a large rimmed baking sheet. Roll the dough from the center outward on the parchment to form a 14-inch diameter circle. (Don’t fret about making a perfect circle, but try to maintain an even thickness.) Transfer the parchment and dough to the baking sheet (the dough will hang over the edges at this point).

留下一个2英寸的边界,均匀传播韭菜mixture in the center. Stir the potatoes, then lift from the bowl, leaving behind any liquid, and distribute evenly over the leek mixture, overlapping the slices. Tuck any irregularly shaped potato slices under or between the more perfect rounds, making sure to maintain the 2-inch border. Dollop the ricotta over the potatoes, and sprinkle with 1/2 tsp. flaky sea salt and the remaining 1/2 tsp. lemon zest, topping each dollop of ricotta with a small pinch of salt and lemon zest. Top the filling with the provolone, the remaining 1/2 tsp. rosemary, and a grind of fresh pepper.

Fold the edge of the dough up and over the filling, pleating it as you go. If the dough sticks to the parchment, refrigerate for 5 to 10 minutes, then continue folding. Brush the folded edge with the egg wash, and sprinkle with 1/2 tsp. flaky sea salt.

Bake, rotating the baking sheet halfway through, until the crust is golden brown, the cheese is golden in places, and the potatoes are tender, 45 to 60 minutes. if the top of the galette is browning too quickly, tent with foil and continue to bake until the potatoes are tender. Transfer to a cooling rack, and let cool for about 10 minutes. Serve warm or at room temperature.