Preheat oven to 350 degrees F.

Line cupcake pan with liners and set aside.

Sift together flours, baking powder, salt, and cinnamon into a medium bowl and set aside.

In a large bowl or stand mixer fitted with a paddle attachment, cream the butter and sugar until pale and fluffy on medium-high speed.

Add eggs one at a time mixing between each addition.

Add vanilla, scrape down the sides as needed.

On low speed, add the flour in in small batches alternating with the milk and heavy cream.

Add in the sour cream and beat until combined.

Fill liners ¾ of the way full and bake for 18-20 minutes until toothpick comes clean.

Transfer to a cooling rack to finish cooling.

Once cool, melt butter and dip the dome of the cupcakes in it and then into the cinnamon sugar.

In a large bowl or stand mixer fitted with a paddle attachment, cream butter and sugar on low speed until pale and creamy.

Slowly add in confectioners' sugar and heavy cream a little at a time, alternating between each, while mixing on low over the course of about 3 minutes.

Add vanilla, cinnamon and salt and beat on medium speed for about 3 minutes until light and fluffy.

Frost cupcakes and sprinkle with cinnamon sugar.