Make the crumble topping

1. In a medium bowl, add the flour, almond meal, brown sugar, cinnamon, and fleur de sel. Mix with a spoon until combined.
2. Add the cold butter cut into small cubes. Using your fingertips, rub the butter into the dry ingredients until you get a crumbly mixture with small clumps.
3. Do not overwork it. You want a sandy texture with visible crumbs.
4. Cover the bowl with plastic wrap and place it in the refrigerator while you prepare the rest of the pie.

Make the pie crust

1. In a large bowl, mix the flour, powdered sugar, and salt.
2. Add the very cold butter cut into small pieces. Using your fingertips, rub the butter into the flour until the mixture looks sandy, with some pea-size butter pieces remaining.
3. Pour in the ice-cold water a little at a time and gently bring the dough together with your hands.
4. Do not knead. Stop as soon as the dough forms a ball.
5. Wrap the dough in plastic wrap and refrigerate for 20 minutes. This helps the crust stay flaky.
6. After chilling, roll out the dough between two sheets of parchment paper or on a lightly floured surface until about 3–4 mm thick.
7. Grease a 9-inch (22–24 cm) pie pan and gently place the dough inside.
8. Press it into the corners, trim the excess, and place the pie pan back in the fridge while you prepare the filling.

Prepare the apple filling

1. Peel, core, and slice the apples.
2. Place them in a large bowl and add the brown sugar, vanilla extract, lemon juice, flour (or cornstarch), and cinnamon.
3. Mix gently with a spoon until all the apple slices are evenly coated.

Assemble and bake

1. Preheat the oven to 350°F / 180°C.
2. Remove the pie crust from the fridge and fill it with the apple mixture, arranging the apples evenly and pressing them down slightly.
3. Take the crumble topping from the fridge and sprinkle it generously over the apples, making sure they are fully covered.
4. Place the pie on the middle rack of the oven and bake for 55 minutes to 1 hour, until the topping is golden and the filling is bubbling.

Cool and serve

1. Remove the pie from the oven and let it cool completely at room temperature.
2. This step is important so the filling can set properly.
3. Serve warm or cold, plain or with vanilla ice cream or whipped cream.