For The Cake, Place A Rack In The Center Of The Oven, And Preheat The Oven To 325°F.
Grease And Flour Two 9″ Round Cake Pans With Vegetable Shortening And Flour, And Shake Out The Excess Flour.
Set The Pans Aside.
Place The Sugar And Oil In A Large Mixing Bowl, And Beat With An Electric Mixer On Medium-Low Speed Until Creamy, About 30 Seconds.
In A Separate Bowl, Sift Together The Flour, Baking Soda, And Salt.
Add A Third Of The Dry Ingredients To The Oil And Sugar Mixture, Blending On Low Speed Until Combined.
Add Half Of The Buttermilk And Blend Until Incorporated.
Add Another Third Of The Dry Ingredients And Blend, Followed By The Remaining Buttermilk, And Finally The Last Third Of The Dry Ingredients Until Incorporated.
Stir In The Mincemeat, Walnuts, And Bourbon Or Other Liquid.
Divide The Batter Between The 2 Prepared Pans, And Smooth The Top With A Rubber Spatula.
Place The Pans In The Oven And Bake Until The Top Springs Back When Lightly Pressed With A Finger, 53 To 58 Minutes.
Remove The Pans From The Oven, And Place Them On Wire Racks To Cool For 10 Minutes.
Run A Sharp Knife Around The Edges, Give The Pans A Gentle Shake, And Invert The Layers Once And Then Again Onto The Racks So They Cool Right Side Up.
Meanwhile, Make The Icing.
Place The Brown Sugar, Butter, Cream, And Salt In A Large Saucepan Over Medium Heat.
Stir And Bring To A Boil, Then Reduce The Heat And Let The Mixture Simmer, Stirring Occasionally, Until Thickened, 5 To 7 Minutes.
Stir In The Baking Powder And Vanilla, And Let The Mixture Cool Slightly, Then Beat Vigorously With A Wooden Spoon Until The Mixture Thickens, About 1 Minute.
Add The Confectioners’ Sugar, And Stir Until The Frosting Is Of Good Spreading Consistency.
It Will Harden Up From This Point On, So You Need To Work Quickly.
To Assemble, Place 1 Layer On A Cake Platter And Ladle Over About 1 Cup Of The Frosting, Smoothing Across The Top.
Place The Second Layer On Top Of The First, And Ladle The Remaining Frosting Over The Top, Letting It Fall Down The Sides Of The Cake.
While The Frosting Is Warm, Press The Chopped Walnuts On Top Or Onto The Sides Of The Cake, If Desired.
Let The Cake Rest For 20 Minutes Before Slicing.
