What are the best gluten free flours to create a homemade flour blend for pate choux? A crispy tollhouse cookie without a sandy texture?

Here's my dough for churros. That's the most successful I've been with GF pate choux. It doesn't bake as well as it fries. Sorghum flour lends a slightly more gritty texture than brown rice flour, so you may want to use brown rice flour in its place if you're quite opposed to sorghum.

1/3 cup sweet rice flour
¼ cup sorghum flour
2 Tbls tapioca flour
½ cup water
¼ cup DF butter
1/8 tsp salt
1 egg

Mix together flours in a separate bowl and set aside. In a pot over medium heat, bring water, DF butter, and salt to a rolling boil, stirring to melt butter. Reduce heat to low and mix flours into water, stirring quickly, until dough forms into a ball and butter seems thoroughly mixed in. Remove from heat. Beat egg in a separate bowl, then add slowly to dough, mixing until dough becomes uniform.

Have you tried garbanzo bean flour? Potato flour? I use 25% rice flour in my shortbread cookie dough (it's not a gluten-free cookie) as well as sometimes in a pâte sucrée because I like its subtle crunch. But my crunch may be your gritty, and I can understand why you would want a chocolate chip dough that isn't that.

My favorite is:
1 cup brown or white rice flour
1 cup sweet rice flour (mochi)
2-4 Tbls tapioca starch

That should give you a really nice tollhouse cookie texture. Sometimes I'll increase the brown rice flour slightly (by 1/4 cup) if a cookie dough seems too wet.

As for pate choux, the same flour blend can give you decent results, but not spectacular. I'm still working on this one. I can tell you that increasing the amount of eggs (usually by 1) often yields better results.

Above all else, avoid using any bean-derived flours. They add protein, yes, but the flavor and texture will never be stellar if you use those. Stick with rice flours, millet, potato, and buckwheat.