Fresh Strawberry Slab Pie

Ingredients

• 5 cups (640 grams) all-purpose flour, plus more for dusting
• 2 tablespoons granulated sugar
• 1 1/2 teaspoons fine salt
• 2 cups (450 grams) cold, unsalted butter, cut into tablespoon-sized pieces
• 6 to 9 ounces (175 to 265 milliliters) cold, well-shaken buttermilk
• 3 1/2 pounds (1575 grams) strawberries
• 3/4 cup (150 grams) granulated sugar
• 6 tablespoons (50 grams) cornstarch
• 1 teaspoon finely grated lemon zest
• Pinch of salt
• 1 tablespoon fresh lemon zest
• 1 large egg
• Turbinado sugar for sprinkling