Penzeys Chocolate Cake + America's Test Kitchen Frosting

CAKE
Ingredients:
2 cups flour
1/2 cup cocoa powder (Penzeys is the best!)
2 tsp baking soda
1 tsp salt
2 tsp vanilla
1 stick (1/2 cup) butter
2 cups sugar
2 cups boiling water
2 eggs

Directions:
Preheat oven to 350 degrees.  Sift together the flour, cocoa, baking soda and salt. (Note: Sifting is important!  If you don't sift, you will end up with lumps of flour in the cake.)  In a separate bowl, cream together the vanilla, butter and sugar.   Add the boiling water to the creamed mixture, blend, then add the eggs and mix 'til well blended.   Gradually add the dry ingredients and mix well.  Pour into an ungreased 9 X 13 pan and bake for 30 mins.  (Note: this cake batter is extremely runny.  It's not a mistake, that's just the way it is.)

FROSTING
Ingredients:
16 oz semisweet chocolate, finely chopped (Note: do NOT substitute chocolate chips)
8 TBS unsalted butter
1/3 cup sugar
2 TBS corn syrup
2 tsp vanilla
1/4 tsp salt
1 1/4 cups cold heavy cream

Directions:
Melt the chocolate in a heatproof bowl set over a saucepan containing 1 inch of barely simmering water, stirring occasionally until smooth.  (Note: I always just melt the chocolate in the microwave on very low power.)  Remove from heat and set aside.  Meanwhile, heat the butter in a small saucepan over medium-low heat until melted.  Increase the heat to medium; add the sugar, corn syrup, vanilla, and salt and stir with a heatproof spatula until the sugar is dissolved, 4 to 5 minutes. Add the melted chocolate, butter mixture, and cream to the clean bowl of a standing mixer and stir to thoroughly combine.

Place the mixer bowl over an ice bath and stir the mixture constantly with a rubber spatula until the frosting is thick and just beginning to harden against the sides of the bowl, 1 to 2 minutes (the frosting should be at 70 degrees).  (Note: I recommend skipping the ice bath, because it caused my frosting to clump up.  I think the frosting just needs to cool down a bit before you whip it with the mixer.)  Place the bowl on a standing mixer fitted with a paddle attachment and beat on medium-high speed until the frosting is light and fluffy, 1 to 2 minutes.  Stir with a rubber spatula until completely smooth.

Note: This makes a large amount of frosting, so if you just want to frost the top of a 9x13 cake, you can get away with making 1/2 of the recipe.