Mix all the ingredients to make the short crust pastry. Work the dough well out and smooth and let it stand for at least 1 hour in a cold room.
Take a Tarte form and place it on a baking paper. Draw around the form on the paper with a pencil and cut it out. We will need it later!
Butter the Tart form well. That will prevent the dough to stick on the form while baking.
Take out your dough and roll it out to approximately ½ cm thickness. Turn the baking form and place it on the dough. Calculate 2 cm more from the form and cut out all around. 2 cm more are required or your dough will be too short to fit into the baking form.
Place the cut out dough into the buttered form and poke with a fork a few fine wholes into it. Add the previously cut out baking paper on top with some weight such as a handful of beans or lentils. That will prevent the dough to blow up in the center and to stay even. Bake the dough by itself for 15 mins at 180 C.
In the meanwhile prepare the cream. In a bowl mix Butter, sugar smooth. Add the Almond flour, Eggs, Orange Zest and Grand Marnier. Mix it all well so that no lumps are left.
Rinse, peel and cut the Rhubarb into 1 ½ cm thick pieces.
Once the dough is finished baked, take it out and remove the baking paper with the beans/lentils. Fill into the short crust pastry the almond cream mix and arrange the cut rhubarb pieces on top. Bake the Tart for 1 hour at 180 C.
Once finished baked, take out the Tart and sprinkle Sugar on top to garnish.