Wash blueberries and then drain water, but do not pat them dry. Add blueberries to a medium or large saucepan. Make sure your saucepan is big enough and wide enough that the blueberries only fill half the pot (or less). See notes for more details.
Add sugar to the blueberries and stir until the blueberries are evenly coated in sugar. Bring the mixture to medium-low heat, stirring continuously so that the blueberries do not get stuck to the bottom of the pan. If you find your mixture is too dry you can crush some of your blueberries as you stir (only crush about 1/5 of the mixture) to release enough liquid to prevent your blueberries from sticking to the bottom of your saucepan.
When your blueberries release enough liquid to cover a thin layer across the bottom of your saucepan, turn your stove to the lowest heat setting. Sift in the cornstarch with a mesh strainer. You want to sift in the cornstarch because you don't want it to hit the hot mixture in clumps which will cause it to cook clumped up. Working quickly, immediately stir the sifted cornstarch into the blueberry mixture until the cornstarch is fully dissolved in the liquid.
Once the cornstarch is fully mixed in, bring your mixture to back to medium-low heat. Continue to stir and let the blueberries cook until there is enough liquid released that the blueberries are mostly submerged in liquid with only the top layer of blueberries partially above the liquid.
Once there is enough liquid, stop stirring and turn the heat up to medium. Let the mixture come to a simmer. Let the mixture simmer for about 30-60 seconds or until the liquid is thick, like jam or a thick sauce. Turn off heat.
Pour the filling into the graham cracker crust. Use a spatula to smooth and even out the surface. Place pie into fridge until the pie filling is set. This can take 1-2 hours, or leave it overnight. Once pie filling is set you can decorate it or leave it as is. I like to leave it plain and serve it with ice cream.
Notes
When I make this pie, I usually make it with 3/4 cup of sugar. I found that to be just the right sweetness for me. Sweet, but not too sweet. However, for the recipe written I used 1 cup because I found this to be more consistent to how blueberry pie filling usually is (very sweet). If you prefer your desserts a little less sweet, you can reduce the sugar to 3/4 cup.
I have only tested this recipe with fresh blueberries. I think it should work with frozen blueberries but if you are using frozen, make sure to let them thaw first and pat them mostly dry.
If using fresh blueberries, wash them and drain the water but don't pat them dry. That little bit of moisture is needed to keep the blueberries from sticking to the heated saucepan before the berries release their liquid.
Make sure you use a medium to large saucepan (between 3-4 quart) that is also wide (instead of just very tall). Your blueberries should only fill about half the pot. You don't want the blueberries stacked high because it will take longer for the berries on top to heat up and it will be harder to stir and cook the filling. I used a 3 quart saucepan that is 8 inches in diameter.
Make sure you sift in the cornstarch with a mesh strainer. This will help the cornstarch to easily dissolve and not clump up. Also make sure that your saucepan is at lowest heat setting when adding the cornstarch so that the cornstarch does not cook too quickly. You want it to be fully dissolved in the blueberry mixture before turning up the heat again.
The nutrition information provided are only estimates based on an online nutritional calculator. This is not a comprehensive list of all the nutrients in the recipe (i.e., does not include vitamins, cholesterol, etc). I am not a certified nutritionist. Please consult a nutritionist or doctor for accurate information and any dietary restrictions and concerns you may have.