Preheat your oven to 350F and line a cupcake pan with paper liners (this recipe yields 12 cupcakes).
In a medium bowl, whisk 1 ½ cups cake flour, 1 teaspoon baking powder and ½ teaspoon salt. Set aside.
Using a handheld electric mixer or a stand mixer with the paddle attachment, beat ¼ cup butter and ⅔ cup sugar until the mixture is pale and creamy (about 2-3 minutes on medium-high speed).
Add the eggs one at a time ensuring each addition is well incorporated. Scrape the bottom and sides of your bowl as needed.
Add the melted white chocolate and stir.
Switch to low speed and add a third of your flour mixture, half of your milk mixture, another third of your flour, the rest of your milk and finally the rest of your flour - beating well after each addition. Continue to beat until the mixture is smooth and no noticeable lumps of flour remain.
Transfer your batter into each cupcake liner until they are almost full.
Bake for 20-25 minutes or until a toothpick inserted in the middle of a few cupcakes comes out with minimal crumbs
Cool in the pan slightly before transferring to a wire rack to cool completely.
To fill the cupcakes, you can use a Bismarck tip or simply carve a small hole in the middle of your cupcakes about an inch in diameter and spoon a dollop of jam in it (see post for tips on how to fill cupcakes).
Top with frosting (recipe follows) and decorate as desired.
For the White Chocolate Cream Cheese Frosting:
Using a handheld electric mixer or a stand mixer fitted with the paddle attachment, beat your cream cheese portions and ¼ cup butter on medium-high speed until incorporated.
Add a cup of confectioner's sugar a little at a time beating well after each addition.
Add the melted white chocolate and 1 teaspoon vanilla and continue to beat until well incorporated and your frosting is smooth and creamy.
Make sure the cupcakes are completely cool before filling and frosting.
Keep frosting in the fridge if you're not ready to use it yet.
See post for storage instructions, more baking tips and FAQs.