Mix all dry ingredients for the dough in a bowl. Using a dough mixer, blend until it becomes a crumbly mixture, roughly the size of peas. Then, add yogurt and ice water. Quickly knead into a smooth dough with cold hands. Ensure both your hands and the butter remain cold to achieve a crispy crust. Wrap the dough in foil and let it rest in the refrigerator for an hour.
In the meantime, thinly slice the plums and mix them with ground almonds and cornstarch. This helps to bind the plum juices and prevents the dough from becoming soggy.
Roll out the chilled dough evenly and place it on a baking sheet. Sprinkle some cornstarch and ground almonds over the dough - they also help bind the juices. Then, distribute the plums evenly on the dough, leaving an edge.
Fold the edge of the dough over the plums and brush with plum slices. Sprinkle sliced almonds on the dough edge. Finally, sprinkle the plums with some sugar.
Bake at 180 degrees Celsius (fan) for about 30 minutes until the galette is golden brown. The baking time may vary depending on the oven.
Dust with powdered sugar before serving.
