In the bowl of a stand mixer fitted with the paddle attachment, beat butter at medium speed until creamy, 3 to 4 minutes. In another large bowl, whisk together confectioners’ sugar and cinnamon. Gradually add sugar mixture to butter, beating until smooth. Beat in enough milk to make frosting a spreadable consistency. Beat in vanilla.
Recipe by Bake from Scratch at https://bakefromscratch.com/apple-spice-cake/