Place oven rack in center and preheat to 400℉. Gather a rimmed baking sheet and a 16 x 12" sheet of parchment paper.
Place parchment on work surface and dust with flour. Place dough on floured parchment and dust with additional flour. Roll until it just barely overhangs all sides of parchment and is 1/8" thick. Dust with additional flour to prevent sticking while working. Trim dough so edges are even with parchment edges.
To form edge, roll up 1 inch of each end and pinch together to create 1/2" thick border. Transfer with parchment to rimmed baking sheet.
Arrange apples by beginning in a corner. Place the slices with the curved edge towards the corner, overlapping the rows of sliced by half. Dot with butter and sprinkle evenly with sugar.
Bake until bottom of tart is a deep golden brown and apples are caramelized, approximately 45 - 60 minutes.
Meanwhile, prepare the glaze. In medium microwaveable bowl, combine apricot preserves and water. Microwave about 1 minute on medium, until mixture starts to bubble. Strain to remove large chunks of apricot.
When baked, remove galette to wire cooling rack, brush with glaze. If serving immediately, cool for 15 minutes before transferring to cutting board.