Mix flour, icing sugar, vanilla sugar & salt.
Add butter & egg; knead until well incorporated. Form a ball & chill in your fridge for about 30 min.
Clean & trim the plums; cut into halves & discard the pits.
W/ your handheld electric mixer whisk butter & sugar, add eggs & finally the ground almonds.
Preheat the oven to 160° C fan.
Roll out the pastry between 2 sheets of clingfoil (or baking parchment); transfer to the tart form & fit in. (Discard the cling foil.)
Add the almond mess.
Add the plums.
Bake in the oven for about 40 min.
Sprinkle the sugar all over the tart.
Let the tart cool down to room temperature before removing the tart form.