For the crumble topping: Combine the flour, almonds, sugar and a pinch of salt in a small bowl. Drizzle in the butter and use your fingers to fully incorporate. Set aside.
For the galette: Preheat the oven to 375 degrees F. Line a baking sheet with parchment paper.
Stir the cranberry sauce in a bowl with the sugar, cornstarch and orange zest and juice.
Put the pie dough round on the prepared baking sheet. Spread the cranberry mixture evenly over the crust, leaving a 1 1/2-inch border, then fold and pleat the exposed crust to partially cover the filling. Brush the crust lightly with the milk and sprinkle generously with sugar. Sprinkle the crumble topping over the cranberry, leaving a little border exposed.
Bake until the crust and topping are golden brown, about 35 minutes. Cool on a rack before serving.