Line a baking sheet with parchment and pre heat oven at 390 F = 200 C.
Warm up the milk and turn off heat.
Add the seeds from the vanilla sticks and cover with a lid.
In a medium large pot add water, milk (the one without vanilla), butter and a pinch of salt and bring to a boil.
Remove from heat and turn off heat.
Immediately add flour and mix well with a whisk until well combined.
Allow the dough to cool a little then add eggs, one by one, mixing well after each egg is added until fully incorporated. You need the composition to resemble chewing gum and be a bit sticky. If not add one more egg.
Transfer the dough to a large pastry bag fitted with a flower tip. Pipe rounds onto each prepared pan and do a little swirl for a more spectacular result. If you don't have a flower tip: with a spoon, drop a dollop of dough (about the size of a walnut) in the baking sheet but not very close to each other (about 2" apart).
Bake for about 20 minutes. Do not open the oven for the first 15 minutes.
When all dough is done and baked, let the puffs cool completely and cut in half, horizontally.
For the filling: Take the 16 yolks and mix with sugar and flour and beat well then add the vanilla infused milk little by little. Move to a saucepan and boil while stirring continuously with a whisk until stiff. Remove from heat and add butter.
Then make the whipped cream.
Fill the puffs with vanilla cream and whipped cream.