Heat your oven to 350°F (176°C)

On a floured piece of parchment paper, roll out the pastry crust into either a round or rectangular shape. Slide the parchment with crust onto a baking pan or baking sheet.  Set aside.

To make the filling, combine the blueberries with the lemon juice, ½ cup sugar (100g) and flour. Stir to combine well so that the flour is fully absorbed.

Arrange the sliced plums on the pastry crust. Pour over the prepared blueberries, leaving a margin of at least 1” (2.5cm) around the perimeter of the crust.

Fold the crust edge towards the middle of the galette. Don’t worry if some of the fruit is folded inside the crust.  Brush the edge of the crust with the beaten egg. Sprinkle ¼ cup sugar (50g) over the egg wash and the fruit filling. Sprinkle the edge of the galette with the sliced almonds.

Bake the galette for 1 hour in the oven until the crust is golden brown.