Apple Galette

1. FOR THE DOUGH: Process all-purpose flour, instant flour, salt, and sugar together in food processor until combined, about 5 seconds. Scatter butter over top and pulse until mixture resembles coarse cornmeal, about 15 pulses. Continue to pulse, adding water 1 tablespoon at a time until dough begins to form small curds that hold together when pinched with fingers (dough will be crumbly), about 10 pulses.
2. Turn dough crumbs onto lightly floured counter and gather into rectangular-shaped pile. Starting at farthest end, use heel of hand to smear small amount of dough against counter. Continue to smear dough until all crumbs have been worked. Gather smeared crumbs together in another rectangular-shaped pile and repeat process. Press dough into 4-inch square, wrap it tightly in plastic wrap, and refrigerate for 1 hour. Before rolling dough out, let it sit on counter to soften slightly, about 10 minutes. (Dough can be wrapped tightly in plastic and refrigerated for up to 2 days or frozen for up to 1 month. If frozen, let dough thaw completely on counter before rolling it out.)
3. Adjust oven rack to middle position and heat oven to 400 degrees. Cut piece of parchment paper to measure exactly 16 by 12 inches. Roll dough out over parchment, dusting with flour as needed, until it just overhangs parchment. Trim edges of dough even with parchment. Roll outer 1 inch of dough up to create 1⁄2-inch-thick border. Slide parchment with dough onto baking sheet.
4. FOR THE TOPPING: Starting in 1 corner of tart, shingle apple slices into crust in tidy diagonal rows, overlapping them by one-third. Dot with butter and sprinkle evenly with sugar. Bake tart until bottom is deep golden brown and apples have caramelized, 45 minutes to 1 hour, rotating baking sheet halfway through baking.
5. Melt jelly in small saucepan over medium-high heat, stirring occasionally to smooth out any lumps. Brush glaze over apples and let tart cool slightly on sheet for 10 minutes. Slide tart onto large platter or cutting board and slice tart in half lengthwise, then crosswise into square pieces. Serve warm or at room temperature.

PREPARING APPLE GALETTE
1. Roll dough out onto 16 by 12-inch piece of parchment paper.
2. Trim dough so that edges are even with parchment.
3. Roll up 1 inch of each edge to create 1⁄2-inch-thick border on all sides. Transfer dough and parchment to rimmed baking sheet.
4. Starting in 1 corner, shingle sliced apples on diagonal to form even row over dough, overlapping each row by one-third.