Pineapple Galette

Blend together flour, salt, sugar, and butter with your fingertips or a pastry blender (or pulse in a food processor) just until mixture resembles coarse meal with some small (roughly pea-size) butter lumps. Drizzle with 3 tablespoons ice water and gently stir with a fork until incorporated.
Squeeze a small handful: If it doesn't hold together, add more ice water, 1/2 tablespoon at a time, stirring (or pulsing) until just incorporated, then test again. (Don't overwork, or pastry will be tough.)
Turn out dough onto a lightly floured surface and divide into 4 portions. With heel of your hand, smear each portion once or twice in a forward motion to distribute fat. Gather dough together, with a pastry or bench scraper if you have one, and form into a 6-inch disk. Chill, wrapped in plastic wrap, until firm, at least 1 hour.
Preheat oven to 350°F with rack in middle.
Roll out dough on a lightly floured surface with a floured rolling pin into a 15- by 11-inch rectangle and transfer to a large baking sheet. Chill until slightly firm but still flexible, about 5 minutes.
Sprinkle semolina evenly over dough, leaving a 1-inch border all around, then arrange pineapple wedges on dough, overlapping them slightly, in 3 lengthwise rows. Brush pineapple with melted butter. Mix together sugar and cinnamon and sprinkle over pineapple. Fold border of dough inward over outer edge of pineapple and brush with milk.
Bake galette 30 minutes, then cover loosely with a sheet of foil and bake until filling is bubbling and pastry is golden, 25 to 30 minutes more.
Discard foil and cool galette, uncovered, on baking sheet on a rack 20 minutes, then slide off baking sheet onto rack to cool completely.