For the frangipane cream: In a stand mixer bowl, cream the softened butter and powdered sugar using the paddle attachment. Add the ground almonds, flour, and salt, and mix into the butter mixture.

Finally, add the vanilla and eggs, and mix until smooth. Set aside.

Cut the apples into cubes and toss with the juice of half a lemon. In a small saucepan, make a light caramel with the sugar, then add the butter and apple cubes. Cook for 5 minutes, then drain the apple cubes in a strainer set over a bowl.

Brush the phyllo sheets with melted butter and lightly dust with powdered sugar, layering them and slightly offsetting each sheet.

Carefully fit the layered phyllo sheets into the metal ring, pressing them gently into the bottom and sides. Spread the frangipane cream over the bottom, then scatter the apple cubes, a sprinkle of cinnamon, and the walnut halves. Fold the excess phyllo over the filling to close.

Brush the top with melted butter and sprinkle the crumble over the surface. Bake in a preheated oven at 350°F (180°C) for about 30 minutes. Remove the metal ring before the tart cools.