Preheat oven to 350° F. Prepare cupcake pan - place a sheet of aluminum foil over the top of the pan. Cut "X" shapes in the top of the foil over each cupcake cup. Place one ice cream cone in each slot. (See: Tips)
In a large mixing bowl, whisk together all-purpose flour, granulated sugar, baking powder, and salt.
Add room temperature milk, vegetable oil, sour cream, egg, and vanilla extract. Whisk to combine. Do not overmix.
Add in rainbow sprinkles and mix in until they are dispersed throughout the batter.
Portion the cupcake batter into the ice cream cones. Each standard ice cream cone will need 2½ tablespoons of batter. If you are using cookie scoops, this is equivalent to one small scoop (1 tablespoon) and one medium scoop (1½ tablespoons).
Bake for 20-25 minutes until the tops of the cupcakes bounce back slightly when touched.
Remove from the oven and cool the ice cream cone cupcakes in the pan to room temperature.