Preheat oven to 350°F. Grease cake pan(s) well.
In a medium bowl, whisk flour, baking powder, cinnamon, baking soda, and salt in medium bowl to blend.
Using an electric mixer, beat butter in large bowl until creamy, 2-3 minutes.
Gradually add sugar, beating until fluffy, 1-2 additional minutes.
Beat in eggs, 1 at a time, then add egg yolk. Add rum.
In a small bowl, stir buttermilk with lemon juice and zest.
Reduce mixer speed to low and beat dry ingredients in 3 additions alternately with milk mixture.
Add batter to cake pans, being careful to not fill too full (only to about 2/3rds mark)
Bake cake until tester inserted into center comes out clean, about 25-35 minutes pending pan size . Cool in pan for 10-20 minutes. Turn out onto rack and cool completely.
To prepare glaze: in a small bowl, add sifted powdered sugar and beet juice. Stir to mix. Set aside.
In mixer with medium size bowl and whisk attachment, beat the whipped cream on medium-high until the cream begins to thicken, but only just a bit.
Add sugar and beet juice. Mix until smooth and creamy.
Drizzle over cooled cakes. Garnish with various sprinkles/toppings if you like. Enjoy!