Slice the apples very thin, approximately 1/8" thick. Squeeze the juice of half a lemon over the sliced apples to prevent them from browning.
Dust counter with a little flour. Sprinkle some flour onto rolling pin. Roll pastry out into a rectangle. Fold and crimp edges of pastry about 1 inch on each side to make a 1/2" border. (Crimping the border prevents the folded edges from coming undone while in the oven.) Transfer pastry dough onto a baking sheet lined with parchment paper.
Preheat oven to 400°F.
Start in one corner with the sliced apples and overlap the slices so that they cover about half of the previous row. Continue to overlap apples in rows until the apples cover the entire pastry. Sprinkle the softened butter over the apples. Sprinkle the sugar over the apples. Place pastry in the oven and bake until the tart is deep golden brown and the apples are caramelizing, about 45 to 60 minutes.
Mix the apricot preserves with water and either microwave or place in a small pot under low heat on the stove until it is warm. Strain the preserves. Brush glaze onto the apples and cool. With a piece of parchment paper, cover the apple part of the Galette, leaving the edges exposed. Dust edges with powdered sugar. Cut the Galette in large squares and serve.
Prep Time: 10 minutes
Inactive Prep Time: 10 minutes
Cook Time: 45-60 minutes
This recipe may appear slightly modified from what you've seen on television.