Preheat your oven to 350 degrees F and line 12 muffin tins with paper liners or spray them with non-stick baking spray. 

In a large bowl, whisk together the flour, sugar, baking powder, and apple pie spice.

Add the vegetable oil, milk, eggs, and vanilla and whisk until no large lumps remain. 

Divide the batter between the muffin tins, filling each one about ⅔ of the way full (I use a ¼ cup cookie scoop to ensure they’re all the same size). Set the cupcakes aside while you make the streusel. 

In a small bowl, combine the flour, butter, and sugar. 

Sprinkle about 1-2 teaspoons of the streusel over each cupcake. 

Bake for 15-17 minutes, or until a toothpick inserted into the center comes out clean. 

Transfer the cupcakes to a wire rack to cool while you make the filling and frosting. 

Add the apples, brown sugar, butter, and apple pie spice to a small saucepan set over medium heat. 

Cook, stirring often, for 10-12 minutes or until the apples are soft and the sauce has thickened into a caramel consistency. 

Set aside until ready to use. 

Add the butter and vanilla to the bowl of a stand mixer fitted with the paddle attachment. Beat the butter on medium speed until it is smooth and creamy. 

With the mixer on low speed, slowly add the powdered sugar and apple pie spice a little at a time. 

Once all of the powdered sugar has been added, scrape down the sides of the bowl and turn the mixer to medium-high speed. 

Beat the icing for 2 minutes, or until it is smooth and fluffy.

Transfer to a piping bag fitted with your choice of tip (I used a Wilton 2A) and set aside until ready to assemble. 

Once the cupcakes have cooled, scoop a small hole out of the center of each one. 

Fill the holes with the apple filling (about 2 teaspoons) and place the cake back on top. 

Pipe the icing on top and garnish with a sprinkle of cinnamon. 

Store any leftover cupcakes in an airtight container in the fridge for up to two days.