Follow these simple steps to create your own Whimsical Unicorn Berry Pie:

1. Preheat the Oven: Preheat your oven to 375°F (190°C).
2. Prepare the Berries: In a large mixing bowl, combine the strawberries, blueberries, and raspberries.
3. Mix Ingredients: Add sugar, cornstarch, lemon juice, and vanilla extract to the berries. Gently toss to combine, ensuring the berries are well coated.
4. Prepare the Pie Crust: Roll out your pie crust and fit it into a 9-inch pie pan. Trim any excess crust hanging over the edges.
5. Fill the Pie: Pour the berry mixture into the prepared pie crust, spreading it evenly.
6. Create a Lattice Top: Roll out another piece of pie crust, then slice it into strips. Create a lattice pattern on top of the berries.
7. Apply Egg Wash: In a small bowl, whisk together the egg and milk. Brush the egg wash over the lattice crust for a golden finish.
8. Bake: Place the pie in the preheated oven and bake for 40-45 minutes, or until the crust is golden and the filling is bubbling.
9. Cool the Pie: Allow the pie to cool for at least 30 minutes before slicing. This allows the filling to set properly.
10. Garnish: Just before serving, sprinkle rainbow sprinkles over the top for an extra whimsical touch.

These steps will guide you in creating this incredible pie effortlessly, ensuring that every detail is just right!