Pre-Cooking Prep
Preheat oven to 350°F (175°C).
Grease and line two 8-inch round cake pans with parchment paper.
Mix cinnamon and sugar for the topping; set aside.
Bring butter, eggs, and milk to room temperature.
Make the Cake Batter
Cream butter and sugar until light and fluffy, about 2–3 minutes.
Add eggs one at a time, mixing well after each addition.
Mix in vanilla extract.
In a separate bowl, whisk together flour, cream of tartar, baking soda, cinnamon, and salt.
Add dry ingredients to the wet mixture, alternating with milk, mixing just until combined.
Bake
Divide batter evenly between prepared pans.
Sprinkle cinnamon sugar evenly over the tops.
Bake 25–30 minutes, or until a toothpick inserted comes out clean.
Cool in pans for 10 minutes, then transfer to wire racks to cool completely.
Make the Frosting
Beat butter until smooth.
Gradually add powdered sugar, then vanilla, cinnamon, and cream.
Beat until light, fluffy, and spreadable.
Assemble
Place one cake layer on a serving plate and frost the top.
Add second layer and frost the top and sides.
Finish with an extra sprinkle of cinnamon sugar if desired.