Chances are the dough is too wet and runny. When you pipe out the batter, it probably didn’t hold its shape (see the picture above – the runny batter kind of spreads out). That means it has too little flour, or too much liquid in the form of water, eggs and/or butter. So it doesn’t rise as much, and the little that they rise will deflate when they come out of the oven.
Also the addition of completely dissolved salt apparently helps prevent cracks from being formed on the shell...
Many recipes call for choux pastry to be baked at two different temperatures. First at a higher temperature for a few minutes, and then finish off at a lower temperature. The reasoning behind this is that the higher temp. facilitates the rise of the pastry because the high heat causes the water to evaporate faster, thereby raising the pastry faster and higher. Then the temperature is lowered and the pastry is allowed to dry out and bake properly.
While the theory maybe sound and it may work for some, I found that cooking choux pastry at one set temperature the whole way through, produced more consistent results with a smooth top and minimal cracks.
Michael Ruhlman’s ratio by weight for choux pastry is 2:1:1:2 of water, butter, flour and eggs. While this works well, I found that adding a little extra flour (when using AP flour) helps make the choux pastry that much more crisp – a very desirable result.
When you add flour to the boiling butter-water mix, you need to mix in the flour well (flour needs to absorb all the moisture of the butter-water mix) and then cook it further on the stove so that enough moisture evaporates so you get a good dough. A lot of recipes will talk about the dough leaving the sides of the pan when you’re mixing it, or looking like mashed potatoes or leaving droplets of oil on the surface, as signs that indicate a good dough.
Apart from all that here’s what I look for. When I mix in the flour, it forms a ball and leaves droplets of oil on the surface of the pan as I mix the dough. Additionally, if I were to stick a spoon in the dough it’ll stick and stay upright in the dough as shown in the picture below. If the spoon doesn’t stay up like that, that means there’s still too much liquid/moisture in the dough. This is what I call the “spoon test”.
When you add flour to the boiling butter-water mix, you need to mix in the flour well (flour needs to absorb all the moisture of the butter-water mix) and then cook it further on the stove so that enough moisture evaporates so you get a good dough. A lot of recipes will talk about the dough leaving the sides of the pan when you’re mixing it, or looking like mashed potatoes or leaving droplets of oil on the surface, as signs that indicate a good dough.
Apart from all that here’s what I look for. When I mix in the flour, it forms a ball and leaves droplets of oil on the surface of the pan as I mix the dough. Additionally, if I were to stick a spoon in the dough it’ll stick and stay upright in the dough as shown in the picture below. If the spoon doesn’t stay up like that, that means there’s still too much liquid/moisture in the dough. This is what I call the “spoon test”.
I use either the Wilton 1A Round Tip or Wilton 2A Round Tip for my profiterole pastries...
And another trick I use to get the choux pastry shells to expand even more is to spray the baking tray with some water! It’s simple, yet it works brilliantly. As the water on the baking tray evaporates from around the dough, it helps “raise” the dough from the outside while the moisture IN the dough, helps raise it from the inside.
So just a light spray of water on the baking sheet gives the dough a little extra boost – especially if you use extra flour. Probably because extra flour = extra gluten = so more rise.
When the choux pastry comes out of the oven (after it has been baked to a nice golden brown, crisp shell), use a toothpick to pierce each shell. This lets out any moisture trapped inside, without causing the shell to collapse.
https://www.theflavorbender.com/how-to-make-perfect-choux-pastry/