Preheat the oven to 375 degrees F (190 degrees C).
Line a baking sheet with parchment paper.
In a medium bowl, mix the raisins and currants.
In a small bowl, whisk together the flour and salt.
Cut in the butter until it is crumbly.
Stir in the sugar until well combined.
Add the eggs one at a time, mixing well after each addition.
Stir in the vanilla extract.
Pour the batter into the pie crust.
Place the apple on top of the batter—dot with butter.
Sprinkle with flour mixture.
Bake for 50 minutes or until a toothpick inserted into the center comes out clean.
Let cool on a wire rack before serving.