Preheat the oven to 200 degrees Celcius convection heat.
Rub the butter into the flour. You can do it by hand or on a machine. I always do it in a food processor, it's easy and fast.
Then add sugar, baking powder, and vanilla and mix well.
Quickly combine the dough with the egg. The dough should not be kneaded!
If the dough is very soft, it can be put in the fridge before the kammerjunkere is formed, but if you can work with the dough as it is, it is not needed.
Divide the dough in half, and roll each piece into a long shape on a floured board. Cut each dough stick into about 25 pieces, and roll the pieces into round balls.
Place the kammerjunkere on a baking sheet lined with baking paper with little space between them. Give the kammerjunkere a light pressure so that they become slightly flat.
Bake the biscuits for the first time for 8 minutes at 200 degrees Celcius convection heat.
Take out the kammerjunkere and turn the oven down to 160 degrees Celcius convection heat.
Allow the baked kammerjunkere to cool slightly. When you can touch them, divide them in the middle with a serrated knife. Then place them back on the baking tray with the cutting surface facing up.
Bake the kammerjunkere a second time for 10-15 minutes at 160 degrees Celcius convection heat until crisp and golden.
Allow the finished kammerjunkere to cool completely on a rack before packing in an airtight container.