Make the crust dough. In a bowl, whisk flour, salt, and coconut sugar. Cut in cold butter with a pastry cutter or your fingers until a shaggy, pea-sized crumble forms. Sprinkle in ice water, 1 tablespoon at a time, tossing until the dough just holds together when pressed.

Chill the dough. Form into a disk, wrap, and refrigerate 30–45 minutes. This helps prevent shrinking and keeps the crust tender.

Prep the filling. In a large bowl, combine blueberries, maple syrup, lemon juice, zest, vanilla, arrowroot, and salt. Toss until the berries look glossy and the starch is evenly distributed. Set aside.

Heat the oven. Preheat to 400°F (200°C) with a rack in the lower third. Place a baking sheet on the rack to catch drips and promote a crisp bottom crust.

Roll the crust. On a lightly floured surface, roll dough into a 12-inch circle. Fit into a 9-inch pie dish, trim overhang to about 1 inch, and crimp edges. Prick the base a few times with a fork.

Optional blind bake for extra crispness. Line crust with parchment and fill with pie weights or dried beans. Bake 10 minutes. Remove weights and parchment. Brush edges lightly with beaten egg if using. This step keeps the bottom from getting soggy, especially with frozen berries.

Make the crumble. In a bowl, combine oats, almond flour, nuts, coconut sugar, cinnamon, and salt. Stir in melted coconut oil and vanilla until clusters form.

Assemble the pie. Pour blueberry filling into the crust and spread evenly. Sprinkle crumble over the top, leaving small gaps for steam to escape.

Bake. Place the pie on the preheated baking sheet. Bake at 400°F for 15 minutes, then reduce heat to 350°F (175°C) and bake 30–35 minutes more, until the topping is deeply golden and the filling bubbles at the edges and through the cracks.

Cool completely. Set the pie on a rack and let cool at least 3 hours. The filling thickens as it cools, giving you clean slices.

Serve. Slice and serve as is, or add a dollop of plain Greek yogurt or a small scoop of vanilla ice cream.