Preheat the oven to 350°F and line a large baking sheet with parchment paper.
Press the two pie crust dough circles together to make a ball, then roll it out into a 12-inch circle. Place it on the prepared baking sheet.
Peel, core, and slice the apples into ¼-inch thick slices. In a large bowl, mix the apples with sugar, flour, and cinnamon.
Pour the mixture onto the center of the dough, spreading evenly but leaving a 2-inch border around the edges.
Fold the 2-inch edges of the dough up over the apples to create a crust border all around.
In a small bowl, mix the topping ingredients with a fork until crumbly, then sprinkle it over the apples.
Bake for 40–50 minutes, until the apples are soft and tender.
Let the galette cool for at least 10 minutes before serving. Top with caramel sauce, ice cream, or whipped cream if desired.