So here's the thing, I think I'm pretty clever, this is my 6th pie, I decided to take a gamble and make up the recipe using the experience I've gained, so far. It turned out SO well, I made it twice!
I started by picking out my filling and measuring out the basic ingredients to get an idea of much would make the desired amount of filling. I then went on to experiment with to iterations of the pine nut pie! Below is what I learned based on a little research and experience - but please feel free to contribute or correct me if I'm wrong.
With pies utilizing squash and fruit as the primary filling, it seemed between 1 1/2 - 2 cups of the primary ingredient is needed, then pureed or mixed with other things. I had to determine whether or not to blend the pignolis/pinenuts with something else or treat them like the "fruit" - since pine nuts are so soft, even when toasted, despite their strong flavor, I decided they were fine as the main ingredient rather than the main flavor within some other base (i.e. ginger flavor in the custard pie). I had an 8 oz bag of pinenuts which measured closely to 1 1/2 cups. I toasted them on a cookie sheet in the broiler on low for about 6 minutes and then watched to they reached the right "brown-ness".
To turn the nuts into a cream filling, I then considered which dry and wet ingredients to use.
I have basically only used two kinds of liquid in most of my pies: cream and eggs. I love cream, I will use it whenever I can. I am also a proponent for using it and whole milk rather than "low fat" alternatives and a quarter cup of heavy or light cream can go a long way to create thick, but fluid wet ingredient base. Egg thickens when cooked and mixes well at room temperature; but whole eggs can get quite dense, so consider using just egg whites or a mixture of the two (I used whites in the first iteration of the pie and just whole eggs in the second - it was too dense with the 2 yolks).
Other wet ingredients to consider: For many fruits, the addition of lemon is warranted; for many squash/winter pies, the addition of honey or molasses; and for yet many other kinds of pies and their saucy garnishes, corn syrup (but I'll let you in on a hint, most of the time you don't need it, BUT if you don't use it you will need to replace it with something of similar viscosity - like honey or an amount of water with boiled sugar).
Most of my favorite pies use between 1/2 to 1 1/2 cups of brown sugar to enhance the fruit; in the case of the cream-based pies, similar amounts of white sugar are used BUT often times if you've got good hardy filling (like several cups of a fruit or squash) you really don't need more than 1/2 a cup of sugar. You can also replace it with things like honey or chocolate chips - instead of an extra half a cup of sugar in the pine nut pie, I added chocolate chips!
Two tablespoons of flour goes a long way with giving your pie some density, but if you are trying to create a filling that is not so fruity and not so custardy - like a peanut butter filling - you are going to need closer to a cup of flour. You will also want to consider how you would lighten a dense, flour-based filling. I often use a teaspoon or two of cream of tartar (NOT to be confused with tartar sauce... which I once sent my husband to the store to get in a last minute pie baking frenzy...) - it has a similar effect as baking soda, especially in addition to egg whites.
I don't know if this belongs with wet or dry because it ought always to be added at room temperature which makes it sweat a bit. Generally you need 1/4 - 1/2 a cup in any given recipe (not including the crust) unless you venture away from the fruity/squashy/savory fillings, which call for more, and lean toward the sugary/custardy/creamy/sweet fillings, which call for less.
My favorites in pie: nutmeg, ginger, and, lately, cardamom! You usually don't need more than a teaspoon of any given spice, but I tend to like my baked goods robust so I generally add an extra dash or two. These are some other good pastry spices I selected from descriptions at realsimple.com: