To make the cupcakes, preheat the oven to 350°. Line two cupcake pans with paper liners.
In a medium bowl, sift together the cake flour, baking powder and salt. In the bowl of an electric mixer, cream the butter and sugar together on medium-high speed until light and fluffy, about 2 minutes. Beat in the eggs one at a time, mixing well and scraping down the sides of the bowl after each addition. Add the vanilla extract and mix well to combine. Add in the dry ingredients alternately with the milk, beginning and ending with the dry ingredients. Stir until just combined.
Divide the batter evenly among the cupcake liners, filling them about 2/3-3/4 full. Bake until golden and a toothpick inserted in the center comes out clean, about 18 to 22 minutes. Remove from the oven and allow to cool for 5 minutes in the pans. Transfer to wire racks to cool completely.
To make the apple filling, heat the butter a medium skillet over medium-high heat. Add the cinnamon and sugar and cook for a minute, until the mixture begins to bubble. Lower the heat to medium and stir in the apples. Mix well. Cook until the apples are somewhat tender, about 10 minutes. Remove from heat and let cool.
While the apple mixture is cooling, use the cone method to remove a chunk from the center of each cupcake, making sure to leave a rim around the top of the cupcake. Fill the holes with the cooled apple mixture. To decorate, top each cupcake with a swirl of vanilla buttercream.