Preheat the oven to 400°F (200°C).
Line a baking sheet or pizza pan with parchment paper.
Unroll the pie crust and place it on the prepared baking sheet.
In a bowl, toss the sliced apples with the brown sugar and cinnamon until evenly coated.
Arrange the apples in the center of the pie crust, leaving about a 2-inch border around the edges.
Dot the apples with the small pieces of butter.
Fold the edges of the crust over the apples, overlapping slightly as you work around the galette.
Bake for 35 to 40 minutes, or until the crust is golden brown and the apples are tender.
Allow the galette to cool for at least 15 minutes before slicing.
Serve warm or at room temperature.