I'm making a 3 tier cake (6,9,12") for my friend this weekend and I'm definitely out of my comfort zone!  I have a 8 qt mixer and I'm planning on using it to all it's glory... :)  

Does anyone have a SUPER easy buttercream recipe they could share that would max out my 8 qt?  I'm going to need enough to fill and crumb coat the cakes (they'll be covered in fondant)....so, I calculated that out to be roughly 13 cups....does that sound right??  Please tell me I can make that in one batch in my 8 qt... :)

I have a 7qt.

A single batch of my buttercream is

1/2 C Butter 

!/2C High Ration Shortening

1tsp Vanilla

1 lb powdered sugar

water to desired consistency 7-11tsp

Mujltiply this by 4 and to reduce the mess I mix

1lb butter

2lb PS

2tsp Vanilla

mis and add water until just mixed

Same for Shortening 

2C shortening

2lb ps

2tsp vanilla

Mix until PS is no longer flying around Might need to add a little water.  Now add the butter mixture.  Mix and add water to desired consistency.  So basically making 1/2 at a time to reduce the mess.  with your 8 quart you might up the portions just a bit.  

I hope this make sense.

My recipe scaled to 8 quart mixer:

9 sticks room temp butter (2 pounds 4 oz)

3 cups vegetable shortening

1/2 cup whipping cream, heated in the microwave til steaming

6 pounds powdered sugar

3 tablespoons vanilla

Combine the butter and shortening.

Using the whisk attachment, mix on low until blended.  Add vanilla and mix on low to blend.

Turn mixer to HIGH speed and whip the butter/shortening/vanilla mixture for 5 minute...the color will become much more white by doing this.

Swith to the paddle beater.  Add all the sugar and cover the mixer with a damp towel.

Mix on low until the sugar is combined...the mixture will appear very dry at first but will become more smooth as it mixes.

Add the hot cream and continue mixing on low until the icing is smooth.

Stop the mixer and scrape down the bowl a few times along the way.

Thin icing with additional hot cream when ready to use is needed.

I can push my 8-qt to four pounds of butter in my Italian meringue BC recipe (it's really full) but FYI I'd need 2-3 batches for a cake that size - it depends on how you torte your layers and how thick you make your filling and icing. Also on what you put in your fillings (mine are often 40% something else (like jam or honey) by weight, so I need less BC to get there, for example).