For the dough: mix flour and ginger powder. Add diced butter and vegetable oil, chop to form crumbs. Pour about a quarter cup of ice water over and form the dough into a ball. Wrap in cling film and refrigerate 1 hour.
Remove pits from cherries, sprinkle with cornstarch and mix well.
Divide the dough into 6 parts, roll each into a not very large thin cake. Put the cherry in the center of the cake, sprinkle with sugar and wrap the edges over the filling slightly overlapping.
Lubricate the dough with yolk. Bake in an oven preheated to 200 ° C on a baking sheet covered with parchment for 25-30 minutes. Serve the tarts hot or cold.