Preheat your oven to 350 degrees Fahrenheit and prepare muffin tins with 18 paper muffin cups.
Add the butter and white sugar to the bowl of your stand mixer and mix on high speed until light and fluffy, scraping down the sides of the bowl a few times.
Continue mixing on high and add the eggs one at a time, stopping the mixer and scraping down the sides of the bowl after each addition.
Combine the flour, cornstarch, baking powder, and salt in a medium bowl and set aside.
Measure the milk and scrape the vanilla bean seeds into the milk, stirring well to combine.
Add the flour mixture and the milk mixture alternatively to the butter mixture, mixing on low speed until everything is added (start and end with the dry ingredients).
Mix on high speed for about one minute to ensure everything is combined.
Divide the batter between the 18 prepared muffin cups and bake at 350 degrees Fahrenheit for about 17-19 minutes.