Follow these simple steps to prepare your apple galette with cinnamon:

1. Preheat the oven to 375°F (190°C).
2. Mix the apple slices: In a bowl, combine the thinly sliced apples with sugar, cinnamon, lemon juice, and a pinch of salt. Toss them together until the apple slices are well coated with the mixture.
3. Prepare the pie crust: Roll out the pre-made pie crust on a baking sheet. Ensure that the edges are even and the crust is flat.
4. Arrange the apple mixture: Place the apple mixture in the center of the crust, leaving a 2-inch border around the edges.
5. Fold the edges: Gently fold the edges of the crust over the apples, pleating as you go to create a rustic look.
6. Brush the crust: Using a brush, apply the beaten egg or plant-based milk over the edges of the crust. This step helps achieve a beautiful golden brown finish.
7. Bake: Place the galette in the oven and bake for 30-35 minutes, or until the crust is golden brown and the apples are tender.