Mix soft butter with sugar about 5 min, add yolk, mix 3 min, add salt and flour, knead till dough is smooth and uniform.
Refrigerate about 30 min.
Remove from the fridge, put into tart baking tray, prick with fork and cover with aluminium foil.
Bake about 20 minutes in preheated oven, in 180 C degrees.
Put cherries into pot, add sugar, lemon juice and water boil 5 min.
In separate dish mix gelatin with 2 tablespoons of water, when it dissolves add to cherries (they should be a bit cooled down, not boiling).
Warm up yogurt over water bath, add vanilla sugar and lemon juice. In separate dish dissolve gelatin in 2 tablespoons of water and add to yogurt.
Put both panna cotta and cherries jelly in the fridge, when they are half stiffened, arrange panna cotta on the shortcrust tart, return to the fridge, after 10-15 min, arrange cherries jelly on the top of the tart.