1. Dough: In a bowl, sprinkle yeast and sugar over milk. Let stand until foamy, about 5 minutes. Whisk in egg and butter until smooth. Stir in flour and salt. Transfer dough to a lightly floured work surface; knead until smooth and tacky but no longer sticky, about 3 minutes. Transfer to a bowl brushed with butter, turning to coat. Cover with a clean kitchen towel; let rise until doubled in volume, about 1 1/2 hours; or refrigerate until doubled in volume, 18 to 48 hours.

2. Topping: Combine butter, sugar, flour, salt, and cinnamon in a bowl; massage together with your fingers until combined. Press into bottom of bowl; cover and refrigerate until firm, at least 1 hour and up to 3 days.

3. Filling: Preheat oven to 350 degrees. Toss apples with sugar, 2 tablespoons flour, and cinnamon. Spread in a single layer on a rimmed baking sheet. Roast until almost tender, about 30 minutes. Stir in blueberries, salt, lemon juice, and remaining 3 tablespoons flour; roast until apples are tender, about 10 minutes more. Let cool 10 minutes.

4. Meanwhile, punch down dough. On a lightly floured work surface, roll out to a 13-inch round. Transfer to a 9 1/2-inch deep-dish pie dish. Fold overhang under itself until flush with edge of plate (do not crimp edges). Loosely cover with towel; let stand until puffy and doubled in volume, about 30 minutes.

5. Increase oven temperature to 400 degrees. Transfer filling to center of dough, gently spreading to sides of dish without compressing dough. Crumble topping into bite-size pieces and sprinkle evenly over filling.

6. Bake just until dough begins to brown, about 15 minutes. Reduce oven temperature to 350 degrees; bake until filling bubbles around edges and crust and topping turn golden brown, 45 to 50 minutes more. (If crust or topping are browning too quickly, tent with foil.) Transfer to a wire rack; let cool completely, at least 4 hours or, loosely covered, up to 1 day. Slice and serve with ice cream.