Reddit mentions of The New Pie: Modern Techniques for the Classic American Dessert: A Baking Book

What? Why sous vide cook apples before baking them into an apple pie??? Three reasons:

1. Pectin begins to break down at 183°F, whereupon apples slices will start to turn into apple sauce. And no one wants an apple sauce pie! In contrast, pectin converts to a more thermostable form if held at 140-160°F for a period of time. This will prevent the apple slices from becoming too soft when subsequently baked to a higher temperature. Yes, you could also do this by cooking on the stove, but obviously sous vide is more controlled.
   
2. Different apples varieties, even the same variety at different times of the year, will release different amounts of juice when cooked. I’ve measured greater than a 2-fold difference in the volume of juice released by freshly picked apples versus the same variety of out of season grocery store apples (the latter released more juices). By sous vide cooking the apples first, the juices can be collected and exactly the right amount of juice can be combined with exactly the right amount of starches to create the perfect pie filling. This will also prevent excess juices from bubbling out of the crust and creating an ugly mess during baking.
   
3. Raw apple slices shrink during baking. Pre-cooking minimizes shrinkage and avoids an unsightly gap appearing between the top crust and pie filling.
   
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   Recipe:
   
   
4. Core, peel and slice (7 mm) approximately 10 Golden Delicious apples on mandolin
   
5. Core and coarsely grate 1 medium Golden Delicious apple
   
6. Retain cores and peels
   
7. Toss slices and grated apple with sugar and other filling ingredients
   
8. Separately vacuum pack apple slices and cores + peels
   
9. Cook in a sous vide water bath at 160°F x 1 hour, then increase to 184°F x 1 hour (times/temperatures based on empirical testing and the optimum may be different for a different apple variety or personal preference)
   
10. Remove bags and let cool slightly, then cut corners of bags and drain juice
    
11. If needed, add apple cider to bring juice to 2 cups total
    
12. Let cooked apple slices chill at least 2 hours in refrigerator
    
13. Dissolve 17 g corn starch and 17 g tapioca starch in juice, add to 28 g melted butter and bring to boil in saucepan over medium high heat, stirring constantly until thickening into clear, dark gel
    
14. Let cool slightly, fold into cold apple slices, then pour on top of bottom crust and continue assembling and baking pie as usual
    
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    Further information:
    
    The Food Lab's Apple Pie, Part 2: Perfect Apple Pie Filling, by J. Kenji Lopez-Alt
    
    https://sweets.seriouseats.com/2011/10/the-food-labs-apple-pie-part-2-how-to-make-perfect-apple-pie-filling.html
    
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    The New Pie: Modern Techniques for the Classic American Dessert (2019), by Chris Taylor and Paul Arguin
    
    https://www.amazon.com/gp/product/0525576444