For top-crust non-breaky-ness, I don't know if you allow any vegetable shortening in the crust mixture, but a little bit of it can increase strength and flexibility enough to decrease breaking. (I am usually a 1.5 sticks butter, 2-3 T crisco type myself.) Egg wash will make the stars shinier, and more impervious to moisture -- maybe egg-wash the undersides! -- but I've not heard that it actually strengthens dough.
I have a constitutional disinclination to pre-cooking the filling of berry pies (I usually do blueberry, although I have some cherries in the freezer I should use up), but without pre-cooking I often end up with a way wetter pie than I am expecting. Except one time when I doubled the amount of cornstarch in a fit of pique, and ended up with a blueberry Jello pie. Very disconcerting mouthfeel, although it tasted fine.
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For top-crust non-breaky-ness, I don't know if you allow any vegetable shortening in the crust mixture, but a little bit of it can increase strength and flexibility enough to decrease breaking. (I am usually a 1.5 sticks butter, 2-3 T crisco type myself.) Egg wash will make the stars shinier, and more impervious to moisture -- maybe egg-wash the undersides! -- but I've not heard that it actually strengthens dough.
I have a constitutional disinclination to pre-cooking the filling of berry pies (I usually do blueberry, although I have some cherries in the freezer I should use up), but without pre-cooking I often end up with a way wetter pie than I am expecting. Except one time when I doubled the amount of cornstarch in a fit of pique, and ended up with a blueberry Jello pie. Very disconcerting mouthfeel, although it tasted fine.