Begin by cutting the unsalted butter into small cubes, then chill it in the refrigerator for about 30 minutes. In a food processor, combine the all-purpose flour, granulated sugar, and salt. Add the chilled butter and pulse until the mixture resembles coarse crumbs. Gradually add ice water until the dough holds together, then divide it into two balls, wrap in plastic, and chill for 1 hour.

Once the dough has chilled, let it sit at room temperature for about 30 minutes. Roll out one ball of dough on a floured surface to about ¼" to ½" thickness. Carefully transfer the rolled dough to a greased 9" pie tin, trimming any excess dough from the edges. Now, chill the crust again in the refrigerator for another 30 minutes to keep it firm.

In a large mixing bowl, combine the flour, brown sugar, granulated sugar, ground cinnamon, and salt. Add the diced Granny Smith apple and sliced strawberries, tossing gently to coat. To enhance the flavor, sprinkle in the lemon zest and pour lemon juice and vanilla extract over the fruit mixture, stirring until all the fruit is evenly coated.

Preheat your oven to 350°F (175°C). Add the fruit filling into the chilled bottom crust, ensuring it’s evenly distributed. Dot the filling with unsalted butter for extra richness. Roll out the second ball of dough for the top crust and roll out decorative elements as desired before placing them over the filling. Bake the pie for approximately 45-50 minutes, or until the filling is bubbling and the crust is golden brown; use foil to shield the edges if they brown too quickly.

For any decorative elements, such as a baked poison apple design, place them on a baking sheet and bake separately for 10-12 minutes until golden. Allow the pie to cool for about 15 minutes before adding these decorations on top for a whimsical touch that enhances your beautiful Strawberry Apple Pie.