How to Make It
Preheat the oven to 350°. Line a 12-cup muffin tin with paper liners. In a medium bowl, whisk the flour with the baking powder and salt.
In another medium bowl, using a handheld electric mixer, beat the butter and the granulated sugar at medium speed until fluffy, about 3 minutes. Beat in the eggs, one at a time, then beat in the vanilla bean seeds and vanilla extract. With the mixer at low speed, beat in half the flour mixture, then all of the milk, followed by the remaining flour mixture, until well combined.
Divide the batter among the muffin cups, filling each about two-thirds full. Bake the cupcakes until a toothpick inserted comes out clean, about 20 minutes. Let cool completely on a wire rack.
In a large heatproof bowl set over a saucepan of simmering water, whisk the chocolate with the butter and corn syrup until smooth; remove from the heat and let cool to almost room temperature, about 5 minutes. Whisk in the sour cream, salt and vanilla. Using a handheld electric mixer, gradually beat in the confectioners’ sugar until smooth.
Spread the cupcakes with the frosting and serve.