1cup(226 g or 2 sticks) unsalted butter,, room temperature
2 ½cups(300 g) powdered sugar,, sifted
Preheat oven to 350° F. Line a cupcake pan with baking cups.
In a medium bowl, whisk together cake flour, baking powder, baking soda and salt. Set aside.
In a large mixing bowl, cream together the butter and sugar until light and fluffy. Add the eggs one at a time, beating well after each addition. Beat in the sour cream, vegetable oil, and vanilla extract.
Gradually add in the flour mixture in three parts, alternating with milk (So it goes flour, milk, flour, milk, flour). Mix until batter is uniform and smooth.
Fill baking cups about 2/3 full and bake for 12-14 minutes, or until a toothpick inserted into the center comes out clean. Remove from the oven, transfer cupcakes to a cooling rack, and allow them to cool to room temperature before coring and frosting.
In a large mixing bowl, whip the butter (with a stand mixer or electric hand mixer) until fluffy, about 5 minutes.
With the mixer on low speed, gradually add in the powdered sugar until completely incorporated.
With the mixer on medium speed, add the vanilla and salt, and beat for a minute, until fluffy. Add milk until desired consistency is reached.
Transfer frosting to a frosting bag fitted with desired tip (I used a large star tip).
Using a cupcake corer or spoon, scoop out a small hole about 1-inch in diameter and 3/4-inch deep in the center of each cupcake. Discard scooped out cake.
Fill each cupcake with about 6 jelly beans. Top the cupcake with buttercream frosting and garnish with additional jelly beans if desired. Serve the same day for best taste.
Store cupcakes in an airtight container at room temperature for up to 3 days.