Prep Your Oven and Pans: Adjust oven racks to the lower-middle and upper-middle positions and preheat to 350°F / 175°C. Lightly grease an 8-inch square baking dish with coconut oil. For easy cleanup, place it on a foil-lined baking sheet.

Line a second baking sheet with parchment paper for the crumble topping.

Mix the Filling: In a large bowl, gently combine all the filling : blueberries, tapioca flour, palm sugar, lemon juice, and cinnamon.

Transfer this mixture to your prepared baking dish and cover it tightly with foil.

Make the Crumble Topping: In a food processor, pulse the almond flour, 1/2 cup (480 ml) palm sugar, vanilla, and salt until just combined (about 5 pulses).

Add the softened coconut oil pieces and 1/4 cup (960 ml) of the sliced almonds. Process until the mixture forms large, crumbly clumps, about 30 seconds.

Add the remaining 1/4 cup (960 ml) of almonds and pulse just twice more to incorporate.

First Bake (The Secret Step!) : Spread the crumble mixture in an even layer on the parchment-lined baking sheet.

Place the crumble on the lower-middle oven rack and the foil-covered fruit filling on the upper-middle rack.

Bake for 15-20 minutes, until the topping is lightly golden and the fruit is warm and glistening at the edges.

Assemble the Crumble: Carefully remove both pans from the oven. Uncover the fruit, give it a gentle stir, and then sprinkle the pre-baked crumble topping evenly over it. Break up any large pieces as you go.

Final Bake and Serve: Place the assembled crumble back in the oven on the lower-middle rack.

Bake for about 25 minutes, rotating the dish halfway through, until the topping is a deep golden brown and the fruit filling is bubbling vigorously around the edges.

Let it cool for at least 10 minutes before serving warm.

Don't over-process the topping. Pulse the food processor just until large clumps form. You want a variety of textures, not a uniform, sandy mixture.