Brush a 12.5-inch (32 cm) tart pan with melted butter. In a bowl, mix the oat flour, coconut flour, almond flour, baking powder, baking soda, salt, and Stevia.

In another bowl, whisk the psyllium husk with the milk. Add the beaten eggs and melted butter, and whisk again. Add this mixture to the flour mixture. Mix and knead to form a ball of dough.

On a sheet of parchment paper, roll out the dough into a 15-inch (38 cm) circle. Place the tart pan upside down in the center of the dough. Using the parchment paper, flip the dough and pan together so the dough is on top of the pan. Press the dough into the bottom and up the sides of the pan. Fold any excess dough from the edges inward and press against the sides. Prick the bottom of the crust with a fork.

APPLE FILLING: Remove the cores from half of the apples and cut them into small cubes. Sprinkle with 1 packet of Stevia, the ground cinnamon, and 1/2 tablespoon lemon juice. Cook in a skillet with 1 tablespoon melted butter. Cover and cook until the apples are soft. Sprinkle with 1 tablespoon oat flour, cook for 2 minutes, then remove from heat. Let cool. Fill the bottom of the tart crust with the cooked apples.

Remove the cores from the remaining apples, cut them into slices, and place in a bowl. Sprinkle with 1 packet of Stevia, 1/2 tablespoon lemon juice, and 1 tablespoon oat flour. Mix well. Arrange the apple slices on top of the tart in overlapping circles.

Brush the remaining melted butter over the apples and sprinkle with ground cinnamon. Bake the tart until the apples are soft and the crust is golden. Let cool. Note: This tart is delicious served warm with a scoop of vanilla ice cream or your favorite ice cream. https://youtu.be/R6M0DQEiekQ