Mix the flour, salt, sugar, yeast and lemon zest in a bowl. Whisk the milk and eggs, gradually mix into the dough, ensuring that the flour absorbs the liquid. Combine the crème fraîche and vanilla sugar, mix in, knead for approx. 10 mins. to form a soft, smooth dough. Cover and leave to rise at room temperature for approx. 1½ hrs. until doubled in size.
Divide the dough into 16 portions, shape into balls. Place 8 balls in a circle on a baking tray lined with baking paper. Make sure they are well spaced out. Halve the remaining balls to create 16 balls again. Place 8 of the balls on the inside of the circle and the other 8 on the outside, cover and leave to rise for a further 1 hr. until doubled in size.
Glaze the brioche with egg, sprinkle with sugar crystals. Bake for approx. 25 mins. in the centre of an oven preheated to 180°C.