For crust: Add first seven ingredients to a food processor. Pulse to mix dry ingredients well. The add cubed butter, pulsing until butter is evenly mixed. Then, drizzle in ice water - pulsing as you go - until dough comes together and away from the edge. Form dough into a disk, dust with tapioca flour and wrap in plastic wrap. Chill for 30 min - 1 hour.
For crumble: In a small mixing bowl add all ingredients, using your hands mix together well - breaking up butter cubes with your fingers - until the dough starts to look like oatmeal cookie batter. Set aside.
For filling: Slice apples thinly and add to a small mixing bowl. Toss gently with cinnamon and maple syrup until all apples are coated. Set aside.
To assemble galettes: Once dough has chilled, remove from fridge and let sit at room temp for 10-15 minutes. “Flour” a surface with tapioca flour. Divide the dough by four equal parts. Roll out each portion evenly to approx. 6-7 inches or so. Assemble apples overtop, leaving t least once inch all around to fold. Fold over crust working each edge at a time. Brush crust with egg wash, then sprinkle coconut sugar overtop apples and crust. Top with cardamom crumble and add to a parchment lined baking sheet. Continue until all galettes are assembled - I made 4 galettes, but feel free to make them whichever size you like, but note the baking time will change.
Bake for 15-20 minutes or until crust is golden browned and “dry” to the touch. Set aside to cool for 10-15 minutes. Serve immediately!