In a small saucepan, whisk flour into milk and heat, stirring constantly, until it thickens. It will be the consistency of a thick pancake batter. It should not look wet at this point.
7 tablespoons all-purpose flour, 1 ½ cups . milk
Remove from heat and let it cool to room temperature.
Stir in vanilla.
1 ½ tablespoons pure vanilla extract
While the mixture is cooling, cream the butter, sugar, and salt together until light and fluffy on medium high, about 5 minutes.
1 ½ cups . salted butter, 1 ½ cups . granulated sugar, Pinch of salt
Then add the completely cooled milk mixture along with the cinnamon.
2 teaspoons ground cinnamon
Beat it for about 5 minutes on medium-high to high until it looks like whipped cream. It may look separated at first, so keep beating it until it comes together and looks like a whipped cream.