Step 1: Preheat your oven to 350°F (175°C).
Step 2: If using a pre-made pie crust, fit it into a 9-inch pie pan. To prevent a soggy bottom, blind bake the crust: place parchment paper over the crust and fill with pie weights or dried beans. Bake for 10-15 minutes, then remove weights and parchment and bake for an additional 5 minutes until lightly golden. Allow to cool.
Step 3: In a large mixing bowl, whisk together the eggs, granulated sugar, and salt until well combined. Slowly whisk in the heavy cream and vanilla extract until smooth. Sift in the cornstarch and whisk until fully incorporated. If using, stir in the lemon juice.
Step 4: Gently fold in the fresh (or frozen, unthawed) blueberries, ensuring they are evenly distributed throughout the custard mixture.
Step 5: Pour the blueberry custard filling into the prepared pie crust. Bake in the preheated oven for 40-45 minutes, or until the custard is set and the top is lightly golden. A knife inserted into the center should come out clean.
Step 6: Allow the pie to cool at room temperature for about 1 hour, then refrigerate for at least 2 hours before slicing. Slice and serve chilled, optionally garnished with whipped cream or additional blueberries.