Strawberry Blackberry Slab Pie

Bahan-bahan (14 porsi)

• 4 cups (500g) all-purpose flour (spooned & leveled)
• 1 and 1/2 teaspoons salt
• 1 teaspoon granulated sugar
• 1 and 3/4 cup (396g) unsalted butter, very cold and cubed
• 3/4 cup (180ml) ice cold water
• egg wash: 1 large egg, lightly beaten with 1 Tablespoon (15ml) milk
• optional: coarse sugar for sprinkling on top
• 4 cups (650g) hulled and chopped fresh strawberries
• 4 cups (500g) halved fresh blackberries
• 1/2 cup (100g) granulated sugar
• 1/4 cup (28g) cornstarch
• 1 Tablespoon (15ml) lemon juice
• 1 teaspoon pure vanilla extract
• pinch salt