Preheat oven to 350°F.
Line a cake pan ( I used a round 8" pan) with parchment paper. Set aside.
Place the apple slices in a large bowl, add the brown sugar, lemon juice, lemon zest, cinnamon, nutmeg, and vanilla. Toss together to coat the apples and stir in the maple syrup. Transfer and arrange the sliced apples in the cake pan.
Cut the bread into pieces and place in a food processor bowl fitted with a steel blade. Pulse until the bread turns to crumbs.
Remove the bread crumbs to a mixing bowl, add the almond flour, cinnamon, sugar, ground ginger, salt and cubed butter.
With your fingertips, rub the mixture to incorporate the butter into the dry ingredients. You should end up with a coarse crumble ( Do not over mix to preserve the texture).
Spread the crumble mixture in an even layer over the apples and press it down lightly with your hands.
Bake for 15 to 20 minutes until golden and bubbling at the edges.
Let the crumble cake cool in the pan ( in order to keep the shape when flipped), run a thin knife around the edges then flip onto the serving plate. Gently remove the parchment paper.
Serve warm or at room temperature. You can serve it plain or add a scoop of vanilla ice-cream or some whipped cream and a drizzle of caramel (optional).
Bon appetit!