How to Make It
Weigh or lightly spoon flour into a dry measuring cup, and level with a knife. Combine flour, semolina, 3 1/2 tablespoons butter, and 1/2 teaspoon salt in a food processor; process until the mixture resembles coarse meal. With processor on, slowly add ice water through food chute, and process just until combined (do not form a ball). Gently press the mixture into a 4-inch circle on heavy-duty plastic wrap. Cover and chill for 30 minutes.
Heat remaining butter in the skillet. Add chopped onion, remaining salt, pepper and fresh thyme and cook until softened. Add wine white to deglaze pan and cook until wine is evaporated.
Unwrap dough, and roll dough into a 14-inch circle on a lightly floured surface. Place dough on a baking sheet lined with parchment paper.
Add onion and thyme mixture on top of dough, leaving a 1 1/2-inch border. Arrange apples on top.
Layer half of the cheese on crust then fold edges of dough over the apples to partially cover. Bake at 400° for 25 minutes or until golden brown. Sprinkle the rest of the cheese on the outside of the crust. Bake an additional 5 minutes or until cheese is melted and golden. Cool for 5 minutes. Cut into 8 wedges.