In a large bowl, whisk together all purpose flour, almond flour, and 1 tablespoon granulated sugar. Add the butter and, using a pastry cutter, two knives, or your hands, work it into the flour mixture until it is the size of peas.
Add ice water a couple tablespoons at a time and stir with a wooden spoon until a shaggy dough begins to form. I used 12 tablespoons of water, it shouldn’t be sticky but should just be enough to hold the dry ingredients together. Towards the end, switch to working with your hands. Work quickly to form the dough into a rough disc.
Wrap the dough in plastic wrap and refrigerate 30 minutes or up to three days.
Preheat the oven to 400ºF.
In a large bowl, add berries, cornstarch, 2 tablespoons granulated sugar, lemon zest and juice, and vanilla extract. Stir gently to combine.
Remove the crust dough from the refrigerator and remove the plastic wrap. Lightly flour a piece of parchment paper or a silicone baking mat as well as the top of the dough. Roll out to about 1/8th inch thick.
Pour the berries onto the dough and even them out, leaving 1-2 inches around the outside. Fold up the edges of the dough, working your way around until the berries are contained in the dough but still open in the middle of the galette.
In a small bowl, make an egg wash by whisking together 1 egg with 1 tablespoon water. Brush around the outside edges of the crust.
Sprinkle the edges of the crust with turbinado sugar if desired.
Transfer the parchment or silicone baking mat with the galette onto a large baking sheet. Bake 45 minutes or until the crust is golden brown and cooked throughout.
Allow to cool at least 20 minutes before cutting and serving warm, preferably with good vanilla ice cream.