Prepare the Pie Dough

1. Place flour, salt, and sugar into the bowl of a food processor and pulse to combine.
2. Slowly add the chilled and cubed butter to the flour mixture and pulse in between each addition until pea-sized lumps form 
3. Continue pulsing and add ice cold water at a slow stream and process until the dough comes together into a ball
4. Remove the dough from the food processor and place on a floured surface
5. Knead the dough until fully combined and reaches the perfect consistency (add flour if needed)
6. Divide the dough in half and wrap each piece with plastic wrap and refrigerate for 30 minutes before using

Prepare the Triple Berry Filling
1. Combine the mixed berries, granulated sugar, salt, cornstarch, lemon juice and lemon zest in a large bowl            2. Toss to fully combine; set aside to assemble the pie 

Assemble Triple Berry Slab Pie  

1. Preheat oven to 375 degrees F and set out a 9x13 baking sheet (¼ sheet pan) 
2. Roll out half of the dough on a lightly floured surface into a 12x15 inch rectangle about ⅛ inch thick and transfer onto a 9x13 inch baking sheet
3. Press the dough onto the pan and into the edges to create a flat surface and trim the excess dough hanging off the edge of the pan
4. Pour the Triple Berry Filling into the pan and spread evenly to cover the dough
5. Sprinkle 2 tablespoons of cubed butter over the fruit filling and press into the fruit
6. Roll out the remaining ball of dough onto a lightly floured surface into a 12x15 inch rectangle and lay it to cover the berry filling
7. Trim the excess dough from the edge of the pan and crimp the dough perimeter of the slab pie to seal the dough
8. Using a small star cookie cutter, cut stars from the top of the slab pie to create a festive design and place the cut out stars on top of the slab pie 
9. Using a pastry brush, brush the egg wash over the top of the pie dough 
10. Bake the slab pie for 45-50 minutes or until the top is golden brown and the filling is bubbling 
11. Remove the slab pie from the oven and allow it to sit at room temperature for 10-15 minutes so the filling can set 
12. Serve and Enjoy! 

*Egg Wash

1 Egg

1 teaspoon Water

Whisk together the egg and water and set aside