Q:

How can I fix hollow cream puffs?

I'm very proud of how my cream puffs turned out. I followed this recipe although I did NOT use any xanthan gum at all. I also substituted Earth Balance for butter.
They rise beautifully and they're only half hollow. They're soft on the inside, possibly slightly undercooked. I'm concerned that if I bake them any longer they might burn. Here are some pics: https://imgur.com/a/mglMU
Which ingredients or steps are responsible for the hollow anatomy of these delicious beauties?
Does anyone have advice for either tweaking the recipe or my cooking time or some other part of my technique to ensure a nice hollow shell?
Recipe details:

1/3 cup + 1tbsp gluten free flour
  2 Tbsp cornflour/cornstarch
  2 xl eggs
  50g Earth Balance in place of butter
  1/2 tsp powdered sugar  

Place 1/2 cup + 2tbsp water in saucepan with butter and heat to a boil that can’t be stirred down.
Add flour mixture of all dry ingredients and mix with spatula until smooth
Remove from heat and allow to cool for 2-3 mins
Add 1 egg and mix until incorporated
Incorporate the second egg
Pipe and bake in a 425°F preheated oven for 25 mins

A:

This recipe uses a substitution for a key structural ingredient (gluten), which is always likely to lead to compromises. If you omit the xanthan, it is even less likely to work, basically it has nothing to hold the structure. Some bakers are happy with the results of such substitutions, but for you the final structure seems to be quite important. 
The first thing you should do is to use the xanthan. If that doesn't help, there isn't much else you can do except try to be perfect in your temperature at every step (while still using the xanthan). 

