Melt butter over medium heat in a medium sized sauce pan.
Stir in 3 tablespoons apple juice, vanilla, apples, cinnamon, brown sugar, and salt.
Bring to a simmer, cover and cook, stirring occasionally, for 4-6 minutes or until the apples have slightly softened.
In a small bowl, whisk together cornstarch and 1 tablespoon apple juice. Slowly stir into the apple mixture.
Continue simmering, uncovered, until the apples are soft and the mixture has thickened, about 2 minutes.
Spoon the apple mixture evenly into the 12 pie dough slots.
Evenly top with the crumb topping.
Bake in prepared oven for 40 minutes, or until the pie crust is golden brown and the filling is bubbly.
Cool for 20 minutes, then remove from the muffin tin and serve with whipped cream or ice cream.